Ipt Project

ACKNOWLEDGEMENTS We would like to express our sincere thanks to Dr. B.N.THORAT, UICT for providing us the platform to do the Inplant Training in HOC,Rasayani without which this project would not have been completed successfully. We would also like to express our since thanks to Mr.A.M.SATHE, HOC for his guidance for carrying out this project. We were really honored for the keen interest he took at each and every step of this work. We would like to express our deepest gratitude for his encouragement and confidence he showed in us while carrying out this project without which this work would have not been completed. We also like to thank Mr. M.S.Patil, for the efforts he has taken to help & guide us. We would also like to thank Mr. Jirimali and Mr.Virkar for the support they had given & faith they have shown in us.

INDEX Sr. No. Contents 1. Introduction to Company 1.1 Company background 1.2 Features of the company 2. Waste heat boiler design 3. Vaporizer design 4. Pressure drop calculations 5. Formaldehyde plant

Pg. No. 3 5 8 13 16

5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 6.

5.1 Formaldehyde-useful industrial product 18 5.2 Introduction Process flow sheet Plant- functional description Equipments used Product sprcification & storage Operational features & critical parameters Material balance Precautions & safety factors Future perspectives

19 20 21 24 30 31 34 42 43

References

44

INTRODUCTION COMPANY BACKGROUND : “HINDUSTAN ORGANIC CHEMICAL LTD.” A leader in Indian chemical industry for over three elected is further expanding its horizons in near future. Earlier company has to depend upon the imports for its vital organic chemical needs till the government with a view to making the company self reliant in this field set up HOC in 1960. Making a beginning as a small chemical unit HOC is today a multi technology, multi-unit company with three fast growing units. HOC has following manufacturing units:The main organic chemical complex at Rasayani in Raigad District (Maharastra) The phenol complex at kochi (Kerala) The poly tetra Flurothylene at Hyderabad (Andhra Pradesh) Initiating an era in basic chemical intermediates. Incorporated at rasayani, a backward area in Maharastra, HOC’s first plant started production in 1970. Between 1970 and 1974 a total of twelve plants were commissioned. Together they produce a large number of products that serve a wide spectrum of industries, ranging from pharmaceuticals to defense and space. After stabilization of the first phase plant in the sixth plan period (1980-85), a number of expansion and diversification plants were launched at Rasayani. Expansion phase included doubling of Hydrogen, Aniline, Nitro Benzene and Nitro Toluene and substantial expansion of Nitroclorobenzene. HOCL was established on 12th Dec.1960 by the Government of India, with the view of making the country self-sufficient in the filed of organic chemical manufacture. Initiating an era in basic chemical complex is a leader in Indian chemical industries manufacturing a wide range of high quality basic organic chemical which are required for variety of chemical and pharmaceutical product such as drugs, medical, dyes, plastics, resins, paints, textile, and explosive.

The company has a continuous manufacturing process and works for 24hrs. A day in 3 shifts in all, around 22 plants are functioning at Rasayani. HOC has its head office situated at Mumbai. The company provides various facilities to its employees like canteen, transport, residential quarter, library and hospital, etc.

FEATURES OF THE COMPANY : Training Centre : HOC has as well-quipped training center, which arranges regular courses for developing skills of employee at all, level. Periodic in house seminars are held, workshop are conducted for employees. Which help them sharpen their skills. Safety department : In everything HOC does, safety of its employees is a prime consideration. This concern is manifest is a multitude of ways. Safety department provide Safety devices to the workers and trains them to work Safety and continuously. Fire department : The fire officer train the personnel to deal with an emergency like fire etc. and teach them to make proper use of fire extinguishers and Safety equipments. Health center : The company health center is well equipped with all the medicines and has its own ambulances. There are qualified doctor in medicals center who examine the workers regularly during the routing medical check up.

Research & Development :

In order to diversify, lower the costs and increase existing capacities, HOC’s R & D efforts are being directed toward assimilation and adaptation of most modern international technologies and development of new and improved processes and chemicals. Scale-up studies are being undertaken through pilot plants, while facilities are being augmented for catalyst testing and sophisticated analysis. In-house research apart, HOC’s R & D division collaborates with scientists from Universities, Institutes of technology and National Research Laboratories, involved in nation building projects. In house in the R & D department has led to the installation of pilot plant for production of cyclohexyl amine. The R& D department is pursuing it’s efforts in the development of noble metal catalyst for increased manufacture of CHA. By recovering resorcinol- a value added chemical from meta amino phenol plant, due efforts of R & D department, HOC has won many prestigious award. Quality Control HOC is very conscious of maintaining a high quality of its products and for this purpose right from raw material through processing to finished product, through checking and stringent tests are carried out at every stage by experts in a modern wellequipped laboratory.

Quality control: HOC is very conscious of maintaining a high product, right from raw materials, to finished products, through checking and experts in a modern wellequipped laboratory carry out stringent test at every stage. Export : What began as an import substitution effort years ago is now an export activity that is steadily gaining momentum. The fact that HOC has generated self-sufficiency in chemicals in India is further complimented by its exports to countries like USA, France, UK, Japan, Germany and many others. Competitive pricing and high quality make HOC’s prospects excellent on the export scene. Today HOC stands as a winner of several awards for excellent export performance from CHEMEXCIL (Basic chemicals, pharmaceuticals and cosmetics export promotion council), an organization set up by the Government of India.

WASTE HEAT BOILER DESIGN : In 1-2 Shell and Tube heat exchanger (WHB), on shell side water flows at 2000 Kg/hr while on tube side HTM oil flows. We have to calculate the steam generation rate. HTM OIL: Inlet temperature of HTM oil = 173oC Outlet temperature of HTM oil = 160oC WATER: Inlet temperature of water = 80oC Outlet temperature of steam = 150oC Following are the physical properties of the concerned fluids: PROPERTIES HTM OIL Ρ, Kg/m3 1000 1000 Cp, Kcal/KgK 0.76 1 µ, Poise 0.3x10-3 K, W/Mk 0.1 0.6

WATER STEAM 1.2 0.47 10-3 1.42x10-4 0.02836

TUBES: Number of tubes = 178 Outer diameter of 1 tube = 1.25in. Thickness = 10BWG Inner diameter of tube = 0.982in. Total heat transfer area for heat exchanger = 117.45m2 Assuming overall heat transfer coefficient, Ud = 240W/m2K Log mean temperature difference is, ∆Tlm = ((173-150)-(160-80))/ln ((173-150)/ (160-80)) = 45.72oC

So, total heat duty will be, Q = Ud A ∆Tlm

= 240 x 117.45 x 45.72 Q = 1288755.36 Watts Now, Total heat duty = Specific heat given by HTM oil Q

= mcp∆Tlm = 1288755.36 = m x 0.76 x (173-160)

HTM oil mass flow rate, m = 24.8 Kg/s = 89,280Kg/hr. HEAT TRANSFER COEFFICIENTS: On tube side: Area of cross section of one tube, a = Π/4x (0.982 x 0.0254)2 = 4.885x 10-4 m2 Velocity, V = volumetric flow rate /area = 24.8 x 2 / (1000 x 178 x 4.885 x 10-4) Number of passes = 2 and number of tubes = 178 V = 0.57m/s. Reynolds number, Re = DVρ/ µ = (0.0249 x 0.57 x 1000)/ (0.3 x 10-3) = 47345

Prandtl number,

Pr = Cp µ/K =

0.76 x 4184/0.1

=

7.026

Nusselt number, Nu = 0.023 Re0.8 Pr0.33 = 0.023 x 473450.8 x 7.0260.33

Since,

Nu = hd/k

So, hd/k = 175.84 h hio

= 706.211 = 554.8W/m2K …………. ( hio = h x ID/OD)

So, heat transfer coefficient on tube side, hio = 554.8W/ m2K Shell side: Square Pitch = 1.5in. Shell area = 1.5” x 1.5” = 2.25sq.in. Tube area = Π/4 x 1.252 = 1.227sq.in. Total tube area = 178 x Π/4 x 1.252 = 218.44sq.in. Shell area = (2.25/1.227)x178 = 326.41sq.in. 326.41 = Π/4x D2s Ds = 20.39in. = 0.518m Baffle spacing = 0.5 x Ds = 0.5 x 20.39 = 10.195in. = 0.258m Equivalent diameter, Deq = 4xflow area/wetted parameter = 4 x (1.52 - Π/4 x 1.252)/ (Π x 1.25) = 1.04 in. Flow area = baffle spacing x clearance x shell ID/pitch

= 10.195 x (1.5 - 1.25) x 20.39/1.5 = 0.0224m2 Velocity, V = Volumetric flow rate / flow area = 2000/ (3600 x 1000 x 0.0224) = 0.0248m/s Reynolds number, Re = DVρ/ µ = 0.0264 x 0.0248 x 1000/10-3 = 654.72 Prandtl number, Pr = Cp µ/K = 1 x 4184 x 10-3/0.6 =7 Nusselt number, Nu = 0.36 Re0.55 Pr0.33 = 0.36 x 654.720.55 x 70.33 hd/k = 89.17 ho = 2026.64 W/ m2K Heat transfer coefficient on shell side, ho = 2026.64 W/ m2K OVERALL HEAT TRANSFER COEFFCIENT: Overall clean heat transfer coefficient (Uc), 1/Uc = 1/ hio + 1/ ho = 1/554.8 + 1/2026.64 = 451.34 W/ m2K Now dirt factor, Rd = 1.785x10-3K/W m2 So, Overall heat transfer coefficient (Ud), 1/ Ud = 1/ Uc + Rd = 1/451.34 + 1.785x10-3

Ud = 242 W/ m2K So, calculated Ud is fairly matching with the assumed value. Now, Total heat duty = (mcp∆T) water + mλ + (mcp∆T) steam 1288755.36 = m x 4184 x (100-80) + m x540x4184 + m x 1967.63x (150-100) m = 0.5278Kg/s = 1900 Kg/hr. So, the required steam generation rate is 1900Kg/hr.

VAPORIZER DESIGN : VAPORIZER :

To check the design for vaporizer : There are 3 zones in the vaporizer. 1.

preheating zone

2.

flashing zone

3.

superheating zone

A) Let UD= 25 w/m2k So, Q = UD A ΔTLM = (m CP ΔT)H2 = 446.42 x 3.46 x 4184 x 4 Q = 7180.74 W 7180.7 = 25 x A x 43.5 A = 6.6 m2…. required area. Provided area = 92.787 m2 B) m cp (160-T)H2

= m λNB

446.2 x 3.46 x 4184 x (160-T) = 2000 x 334720 / 3600 => (160-T) = 0.02877

T = 159.97 oC.

C) Q = m cp (160-T) H2 + m cp (160-T)NB = 446.42 x 3.46 x 4184 x 0.02872 + 2000 x 3.46 x 4184 x 0.02877/ 3600 Q = 1094.3 W Area provided = 0.6823 x 46 = 31.39 m2 Let, UD = 25 w/m2k & we calculate ΔTLM = 41.49 1094.3 = 25 x A x41.49 A = 1.055 m2 Zone Area calculated, m2 Actual area, m2 Preheating 6.6 92.787 Superheating 1.055 31.39

PRESSURE DROP CALCULATIONS : Calculations of pressure drop across 90o bend having 80 mm diameter and with air flow rate 5000Nm3/hr at 9Kg/cm2 and 50oC. Assumptions :

Ideal gas laws such as Boyle’s law are considered to be valid for given air at NTP Data: 1. ρair = 1.2 Kg/m3 2. Head loss coefficient for 90o bend (K) = 1 Solution : 22.4 dm3 of gas at NTP = 1gmol 5000Nm3/hr of gas at NTP = X gmol X = 223214.29 gmol/hr = 6473.2147 Kg/hr Air flow rate at NTP (25oC & 1Kg/cm2 pre.) = 6473.2147 Kg/hr By ideal gas law, V1/T1 = V2/T2 V2 = V1 x T2/T1 V2 = 1.2 x (273.16 + 50) / (273.16+25) = 1.3006 m3 for 1 kg of gas at 50oC

From Boyle’s law, P1V1 = P2V2 V2 = P1V1 = 1 x 1.3006/9 = 0.1445 m3 for 1Kg gas at 50oC and 9Kg/cm2 Now, Density of air at 50oC and 9Kg/cm2, ρair =1/V2 = 6.9204 Kg/m3

6473.2147 Kg of gas = 6473.2147/6.9204 = 935.444 m3 Area of cross section of pipe, A=

d2/4 = 5.0265 x 10-3m2

Velocity, V = volumetric flow rate / A = 935.44/(5.0265 x 10-3 x 1000) = 51.6917 m/s Pressure drop (ΔP), ΔP = ½ ρairV2 K = ½ x 6.9204 x (51.6917)2

x1

= 9245.76Pa ΔP = 0.09248 kg/cm2 Therefore, the pressure drop across 90o bend = 0.09248 kg/cm2 FORMALDEHYDE FORMALDEHYDE – USEFUL INDUSTRIAL PRODUCT: 1. Formaldehyde is useful chemical employed in the manufacture of many industrial product and consumer articles. 2. Formaldehyde is used in the manufacture of phenolic resins, artificial silk and cellulose esters, dyes, organic chemicals etc. 3. Formaldehyde is used as agent for improving the fastness of dyes on fabrics. 4. A major application of Formaldehyde in the manufacture of crop protection and soil disinfections chemicals, fumigants, pharmaceuticals and explosives. 5. It is used for tanning and preserving hides, and for preserving and coagulation of rubber latex.

INTRODUCTION : The current plant - formaldehyde phase 2 produces a 37% water solution of formaldehyde by the vapor phase oxidation of methanol by air in presence of Iron Oxide-molybdenum oxide catalyst in a fixed bed tubular reactor at 320-400°c and scrubbing the gas by D.M. water to absorb HCHO gas(formalin gas to get 37% HCHO. The plant is designed to produce a maximum of 55% HCHO. Alternative ways : Following are the two alternative ways of production of formaldehyde. 1. Silver catalyst process in which methanol is oxidized over a silver catalyst at the atmospheric pressure and 600-650°C. 2. From the Methane by, partial oxidation. But it was found that the process of production of formaldehyde by using Iron-molybdenum oxide catalyst was much more efficient. Hence this process was employed in the plant. Properties : 1. Nature :- colorless liquid with pungent odors. 2. Density :- 1.08-1.085 gm/cm³ (25°C) 3. Boiling point :- 96°C 4. Refractive index :- 1.3746 (20°C) 5. Flash point :- 60°C. 6. Miscible with water, alcohol and acetone. 7. Hazard : - Toxic by inhalation, skin and eye irritant, moderate fire risk. Raw materials : Methanol, air and caustic soda. Utilities : D.M water, cooling water, chilled water, instrument air, power supply. PROCESS FLOW SHEET :

PLANT - FUNCTIONAL DESCRIPTION: The process is accomplished by the oxidation of methanol on a metallic oxide catalyst, using a fixed-bed vapor-phase oxidation converter, according to formula: CH3OH + ½O2 CH2O + H2O ∆H= -159 KJ/mol A low ratio of methanol to air is used to maintain the desired oxidation atmosphere, and the heat of reaction is removed from the converter by boiling a liquid heat transfer medium (Dowtherm A or equivalent medium). The methanol content in air is maintained between about 4 and 9 % by volume. Such a high content can be used because part of stack gas from the plant is recycled, which decreases the oxygen concentration sufficiently to avoid explosive mixtures. The process gives a high yield on a single passage, and also very high conversion making the recovery of methanol from the final product unnecessary. The actual

formaldehyde yield is in the range of 91-94% of the theoretical. The remainder of the methanol is accounted for by unreacted methanol, carbon monoxide, dimethyl ether and a negligible amount of formic acid. The air is supplied by two root type of blowers, here items C-4 A/B. Methanol to the plant is supplied by pump, P-1 and is injected into the air stream after the vaporizer tube bundle through a spray nozzle ring. The air is passed through the methanol vaporizer, E-1, after which the methanol is vaporized. The gas mixture temperature to the reactor is now about 120°C.

The oxidation of the methanol takes place in a fixed-bed reactor with 11878 stainless steel tubes of 21mm. The tubes are loaded with the metallic oxide catalyst to a specific depth. The bottom and the top sections of the tubes are filled with small inert rings to improve the heat transfer.The reactor tubes are surrounded by Dowtherm to remove part of the heat of reaction. The gas mixture entering the top of the catalyst tube is preheated by the boiling Dowtherm in the reactor shell, while passing through the upper inert rings in the catalyst tube. As the gas reaches the heated catalyst, the reaction starts and the temperature rises rapidly to a maximum. When the main part of the methanol has reacted, the temperature drops rapidly again and approaches the temperature of the boiling Dowtherm when the gas leaves the reactor tube. An additional layer of catalyst is loaded below the reactor tubes in the adiabatic bed. The reacted gases pass out of the reactor bottom and back to vaporizer again. On the shell side of the vaporizer the gases are cooled to a temperature of about 110°C, depending on the flow of methanol. The cooled gases then flow to the absorption tower. The absorption takes place in the two columns, T-1 & T-2. The first column consists of a spray section and above that two packed beds. The second column consists of 15 bubble cap trays. Formalin solution of any desired concentration up to 55% can be obtained. The heat of absorption is removed by heat exchanger, E-7 and through cooling water pumped through coils located below the liquid level on each tray. Water is fed into the top of the second absorber and flows counter-current to the gas flow at a desired rate, depending on the formaldehyde concentration of the final product. The reactor shell is filled with boiling Dowtherm in order to obtain the maximum heat transfer rate. The Dowtherm is circulated by thermo siphon circulation through the reactor shell and into the vapor separator, E-3. The Dowtherm vapors are separated from the liquid in the vapor separator from where the liquid flows back to the converter. The vapors are condensed in a tube-and-shell heat exchanger, E-2. During start-up, before the heat of reaction has given sufficient thermosiphon circulation; the Dowtherm is circulated by pump P-2, and preheated in the Dowtherm heater. The Dowtherm condenser is also operated as a steam boil

EQUIPMENTS USED : Following are the equipments used in the plant for the production of formaldehyde. Air blowers, items C-4 A,B : The air blowers, which supply the air for the oxidation process, are Roots type of blowers. The maximum delivery pressure is 88 mbar. The normal air flow is 19200 Nm³/hr, which is achieved with two blowers. The blowers are connected to electrical motors. Different air flows are achieved by changing the pulleys of the blowers. Vaporizer, item E-1 : The vaporizer used is a shell and tube heat exchanger. It works as a flash vaporizer. A flash vaporizer is used because it eliminates the fire hazard; the amount of methanol in the process area is very small. The gas is heated in the vaporizer and after the tube bundle the methanol is sprayed into the gas. Then the gas passed a pack section before it enters the reactor. This part of the vaporizer is equipped with a rupture disc. The temperature of the gas mixture leaving the vaporizer is about 120°C. The heat to vaporize the methanol is taken from the hot gases coming from the reactor. Reactor, item R-1 : The air-methanol mixture enters the top of the fixed-bed reactor, which is equipped with 11878 stainless steel tubes, 21.0 mm inside diameter and 1500 mm in length. The tubes are loaded with the metallic oxide catalyst to a specific depth. The bottom and the top parts of each length of tubes are filled with small inert rings. The purpose of these rings is to improve the heat transfer between the boiling Dowtherm and the incoming gas mixture as well as between the Dowtherm and the exit gas. In this way

the gas mixture is preheated before it enters the reaction zone and the reacted gases are cooled rapidly upon leaving the catalyst zone. The reactor top is also equipped with two rupture discs, six of the reactor tubes are fitted with stainless steel thermocouple wells. Each one equipped with six thermocouples in fixed positions. Below the tubes in the reactor an additional layer of catalyst is loaded, the adiabatic bed. There is no cooling in this part; therefore the temperature of the gas leaving the bed is increased by approx. 10°C Vapor separator, item E-3 : The Dowtherm vapor separator is cylindrical, vertical vessel, located besides the reactor. In the vessel the Dowtherm vapor is separated from the liquid as it is forced from the converter by the thermo siphon circulation. The Dowtherm vapor from the vapor separator is condensed in the waste heat boiler, which is located just above the vapor separator. The liquid Dowtherm in the vapor separator flows back into the converter and again into the vapor separator. The vapor separator is maintained about half-filled or somewhat less with liquid Dowtherm during operation, i.e. when the dowtherm is boiling. Condenser , item E-2 : The Dowtherm vapors from the vapor separator are condensed in a tube-and-shell heat exchanger, which is also operated as a boiler. The boiling water is kept on the shell side. The boiler feed water level in the condenser is controlled automatically by the control loop. Steam of pressure up to 22 Kg/cm² (g) can be produced. The condenser is equipped with a level glass for the boiler feed water level and two safety valves for the steam system. Absorption towers, items T-1, T-2 : The bottom section of the column T-1 contains 6 spray nozzles through which the product solution circulates. By means of these nozzles the walls of the bottom section are continuously sprayed with formalin. This is important in order to prevent precipitation of Para formaldehyde. All nozzles point upwards. The bottom section of the column is also equipped with a steam coil intended for heating primarily in case of an interruption in production. In addition, there is a level glass, a level controller, alarms for high and low levels and temperature indicators. Above the spray section there are two packed beds through which the formaldehyde solution is pumped by means of the circulation pumps. The formaldehyde solution, which is circulating over the upper packed bed, is cooled by an external plate heat exchanger, E-7. The second tower T-2 consists of 15 bubble cap trays, each containing 109 bubble caps. The trays are equipped with cooling coils for removing the heat of absorption. When producing formalin, process water is added to the upper tray in the column T-2 and the amount is controlled by the flow controller.

At the top of the columns there are built-in drop separators for separating any entrainment carried along with the gas flow. In T-1this is only a prolonged pipe and in T-2 a demister of impingement type. A high pH value in the column contributes to more efficient absorption of formaldehyde. For this reason there is a piston pump for adding sodium hydroxide to the process water. To increase the chemical stability of the formaldehyde for storage, stabilizer is added in the outgoing product. Chilled water passes through the cooling coils in the T-2 absorber and back to the chilled water unit. When having colder cooling water, the chilled water is completely or partly replaced with this. Absorption heat is also removed in heat-exchanger, E-7, where circulating formalin from the upper packed bed is cooled with cooling water. Dowtherm system : When the formaldehyde plant is not in operation, the Dowtherm stored is stored in a holding tank, E-6, and kept at a temperature of about 20-40°C, since dowtherm is solidified at a temperature of approximately 12oC. By storing the Dowtherm in this manner, it is possible to cool down the production equipment quickly, and there is no danger of freeing the Dowtherm in the system. When the formaldehyde plant is ready to go into operation, the Dowtherm is brought into the Dowtherm circulating system by means of dowtherm circulation pump. The Dowtherm in the separator is kept at low level in order to allow adequate room for expansion during the heat-up period. When the Dowtherm has reached the operating temperature, the Dowtherm level in the circulating system is adjusted, if necessary, to the proper operating level by adding or removing Dowtherm. During the operation of the plant, the Dowtherm vapor separator is maintained about half filled. The Dowtherm liquid in the separator exerts a hydrostatic head on the Dowtherm in the reactor R-1 and in the ECS heat recovery. In operation the Dowtherm vapor passes out from the top of the converter shell, R-1 and out from the top of the converter shell, and out from the top of the ECS heat recovery, sweeping Dowtherm droplets along with it, and enters the vapor separator. The pressure in the Dowtherm system can be regulated between 0 and 2 kg/cm² (g) by applying instrument air on the tube side of the Dowtherm condenser. The correct pressure is controlled by the controller. The Dowtherm condenser is equipped with a safety relief valve. During the start-up of the plant the heater located in the Dowtherm circulating system is turned on. When the Dowtherm has reached its operating temperature and the methanol feed has been started, the heater is turned off manually. Thermocouples are installed to check that there is no overheating of Dowtherm. N2 system :

In case of a temperature surge, the methanol and blowers are shut off by the safety system. If the temperature still does not decrease, a fire-extinguishing system consisting of three N2 bottles must be manually opened. Emission Control System : The ECS consists of three different items. Item E-15 is a preheater for heating the gases from the absorber to the ignition temperature of the catalyst. Item E-18 is a vessel containing the platinium-catalyst. The catalyst bed which is supported on a screen has a height of approximately 60 mm. The reaction taking place is not cooled, therefore the gas temperature leaving the bed increases.The item E-17 is a tube heat exchanger where the hot gases leaving E-18 is cooled. On the tube side of the heat exchanger the hot gases heat the Dowtherm from the separator E-3. Caustic pump : It has been found that a slight adjustment of the pH in the absorber by adding NaOH improves the absorption of the formaldehyde which is important when producing 55% formalin. When producing formalin, caustic pump can be used for adding NaOH to the process water. The feed rate to the absorption tower depends to some extends on the original pH of the water. However, the caustic forms in contact with formic acid sodium formate. This will increase the ash content in the product. Approximately 5 kg/h of a 5% NaOH-solution can be added which raise the pH at the top on the tower to appr. 9, to keep ash content in the product below 100 ppm. Recycle control valve : As the methanol oxidation to formaldehyde requires oxygen, fresh air must be continuously brought into the plant via the filter. Consequently, stack gas must be emitted via the ECS converter. By recycling about 75% of the exit gases from the absorber, only about 25% of the blower capacity is fresh air. The recycle control valve is positioned so that the oxygen analyzer during normal operation indicates 10.5-11.00 percent by volume of oxygen. PRODUCT SPECIFICATION : Description: - clear and colorless liquid with pungent odor. Concentration: - 37% + 0.5 Methanol content: - 0.5 – 0.8 % Specific gravity at 25/25°C: - 1.097 Acidity: - 0.05% max Iron (as Fe):- 2ppm max. Ash content: - 0.01%max STORAGE : The product Formaldehyde store in the stainless steel tanks at a temperature of 4749°C. With the decrease in temperature and increase in the concentration of aqueous HCHO solution tend to precipitate to Para formaldehyde. At high temperature, the tendency to formic acid increased. Hence the appropriate storage temperature must be maintained. Stabilizer solution methanol serves to inhibit polymer formation. Tank agitation and steam tracing is also provided for preventing Para formaldehyde formation.

OPERATIONAL FEATURES AND CRITICAL PARAMETERS : The plant has been equipped with an interlock system to protect personnel and the environment as well as to prevent damage to the plant itself.

The interlock system controls the process either by shutting off methanol flows to reactor (safety system SWS-B) or airflow from blowers (safety system SS-A). The interlock system is activated if any- predetermined critical limit is reached on the parameters as in the following situations: Methanol flow to the vaporizer is an important control parameter. If there is a high alarm which is alerted at a methanol inlet of vapoarizer. In combination with O2, SS-B will be activated and methanol feed will be stopped. The valve is located very near the vaporizer to ensure that as litttle as possible methanol will enter the vaporizer. The vaporizer top, where vaporization occurs, has a rupture disc connected to safety AB, which stops air and methanol flow to reaction line. The safety system AB activated in case of a too high discharge pressure is obtained from the blowers and hence the blowers and methanol feed are cut off. In case of a pressure surge the reactor; safety system AB to which the rupture disc is connected gets activated in order to shut down the methanol and air to reactor. In the tubular reactor, six of the tubes are fitted with stainless steel thermocouple wells, inside of which are fixed thermocouples. The highest temperature of per chosen thermocouples in each well will alarm if it exceeded the set limit. Safety system SS-D: In plant shut down stage, the dowtherm is stored in a tank where its temperature is maintained between 20-40°C (it solidifies at about 12°C approximately). An electric heater is used to heat the dowtherm about 100°C and hence it avoids water contamination in fresh dowtherm. This heater is connected with SS-D, which automatically shuts off heater incase of a high exit temperature. Oxygen Control: During operation, the O2 concentration of gas going to the reactor is kept constant, by an automatic controller at 11 vol%. This concentration means that approximately 1/3rd of fresh air and 2/3rd of recycle gas from absorber is fed to the reactor. Control of O2 concentration essential. If methanol concentration in the gas to the reactor is below 7 vol%, then no pressure surge will occur, regardless of O2 concentration. However, when the methanol concentration is above 7 vol %, the O2 concentration must be below 13vol% to avoid the risk of an explosion. HCHO Concentration control: A specific concentration profiles is achieved in the absorbers, depending on parameters such as water supply, temperature and the feed gas. If product concentration goes up it means the supply of water is insufficient and must be increased. If the HCHO concentration decreases, then either too much water is being fed or some of the cooling coils in the absorber are leaking. If decreasing the water flow at the top does not reverse the trend of down going concentration, then the coils are to be leak tested. Caustic soda (5%) is also added to the process water in order to achieve better absorption. The pH profile in the absorber is important. At a pH of 8.5, absorption is optional. Formaldehyde pumps and pipelines: All pumps in contact with formaldehyde are always to be drained when not in operation, and thus it assures that no Para formaldehyde formation occurs, which can damage the pumps. All piping in the circulation system for strong formaldehyde solution around the absorber is insulated and steam raced. The insulation is 50mm thick. These actions and control procedures assure that the plant will not produce any hazardous substances and will operate without any interruptions.

Emergency stop : In the control panel there is a red key operated mushroom push button as emergency stop together with a push button with light (reset button). If the emergency stop has been pushed the light in the reset button turns off. To reset the system the key is used to release the emergency stop and thereafter the reset button is pushed in.

MATERIAL BALANCE : General process block diagram :

RECYCLE GAS

COMPOSITION OF AIR : Blower Discharge i.e. Total air flow rate = 18000Nm3/hr And 1 gmol = 22.4dm3 Thus, 18000 Nm3/hr = 803.5714 Kgmol/hr COMPONENTS Kgmol/hr %MOL Kg/hr Wt% N2 677.7116 84.33744 18975.924 83.96472 O2 88.39286 11.0 2828.5714 12.51587 CO 6.402479 0.79675 179.26943 0.793232 DME 1.713954 0.21329 78.841864 0.34886 CH2O 0.062566 0.00779 1.8769821 0.008305 CH3OH 0.586567 0.073 18.770143 0.08304 H2O 28.70139 3.57173 516.62509 2.285964 TOTAL 803.5714 100 22599.879 100 METHANOL FEED: % CH3OH in mixed stream = (A*2240)/ ((32*B) + (22.4*A)) =7.5 Where, A= CH3OH flow rate in Kg/hr B= Air flow rate in Nm3/hr = 18000Nm3/hr Here we get, A = 1930Kg/hr Reactions taking place in Reactor: 92.5 % 1)

CH3OH + 1/2O2

2)

CH3OH + O2

CH2O + H2O 3.5 % CO + 2H2O 1.5%

3)

CH3OH + CH3OH

CH3OCH3 + H2O

4)

0.03% CH3OH + O2

5)

CH3OH

CHOOH +H2O 2.47 % CH3OH

INLET TO REACTOR: Some CH3OH is coming from the blower and some is coming from CH3OH feed, so Total CH3OH in = 1935/32 + 803.5714*0.073/100 Input stream = 60.8995 Kgmol/hr Following are given the amount of CH3OH, O2 used and other compounds formed: In Reaction 1 , CH3OH used O2 used CH2O formed H2O formed In Reaction 2, CH3OH used O2 used CO formed H2O formed

= = = =

56.332Kgmol/hr 28.166Kgmol/hr 56.332Kgmol/hr 56.332Kgmol/hr

= = = =

2.13148Kgmol/hr 2.13148Kgmol/hr 2.13148Kgmol/hr 2.13148Kgmol/hr

In Reaction 3, CH3OH used = 1.82699Kgmol/hr H2O formed = 0.91349Kgmol/hr In Reaction 4, CH3OH used = 0.0182699Kgmol/hr H2O formed = 0.0182699Kgmol/hr In Reaction 5, CH3OH used = 1.50422Kgmol/hr

AT OUTLET OF REACTOR: Outlet of the reactor is used as a heating medium in the evaporator to evaporate methanol. Following is its composition: COMPONENTS

Kgmol/hr

Mol %

Kg/hr Wt%

N2 677.7116 75.71395 18975.92 77.26632 O2 58.0773 6.488397 1858.474 7.567348 CO 8.533947 0.953413 238.9505 0.972961 DME 2.62744 0.293538 120.8622 0.4921218 CH2O 56.3942 6.300361 1691.826 6.888791 CH3OH 1.504207 0.16805 48.13462 0.195995 H2O 90.22772 10.08024 1624.099 6.613019 CHOOH 0.01838 0.002053 0.84548 0.003443 TOTAL 895.0948 100 24559.12 100 This outlet stream of reactor is used for vaporizing CH3OH and in turn to reduce its temperature for better absorption in the two absorbers later. From the absorber we get the required product i.e. 37% Formaldehyde (wt %). From the outlet of reactor 2.5Kg/hr CH2O, 25Kg/hr CH3OH and whole N2, O2, CO and DME goes to T2 outlet thus, CH2O = 1689.326Kg/hr Thus for CH2O to be 37% total amount required (X) is, 1689.326 *100/X = 37 X = 4565.779Kg/hr Water added for absorption is 90.5% of amount of CH3OH feed. Water required to make product 37% by wt = 4565.779-(1689.326+ 23.13462+0.84548) Amount of water in the product = 2852.44 Kg/hr Remaining amount of H2O goes to the T2 stream along with N2, O2, DME, some amount of CH3OH and CH2O. FD PRODUCT OUTLET : COMPONENTS Kgmol/hr Mol% Kg/hr Wt% CH2O 56.31087 26.12778 1689.326 37 CH3OH 0.722957 0.335446 23.13462 0.5067 H2O 158.4689 73.52825 2852.44 62.47478 CHOOH 0.01838 0.008528 0.84548 0.018518 TOTAL 215.5211 100 4565.746 100 T2 OUTLET STREAM : COMPONENTS N2 677.7116

Kgmol/hr 87. 26417

Mol% Kg/hr Wt% 18975.92 87.25446

O2 58.0773 7.478312 1858.474 8.548629 CO 8.533947 1.098872 238.9505 1.099127 DME 2.62744 0.338322 120.8622 0.555943 CH2O 0.083333 0.01073 2.5 0.0115 CH3OH 0.78125 0.100597 25 0.114995 H2O 28.79494 3.707775 518.309 2.384124 TOTAL 776.6098 100 21740.02 100 T2 outlet stream gets divided into two streams which are as follows: 1. 2.

RECYCLE STREAM ECS INPUT STREAM

Amount of fresh air (X) required can be calculated as: (803.5714-X) x 7.478312 + X x 20.3 = 803.5714 x 11 X = 220.7141Kgmol/hr Thus, amount of recycle stream = 803.5714-220.7141 = 582.8573Kgmol/hr Amount of ECS stream

= T2 stream - recycle stream

= 776.6098 – 582.8573 = 193.7525Kgmol/hr EMISSION CONTROL SYSTEM (ECS) : At equilibrium stage, amount of CO generated in reactor system goes to the ECS system while the rest gets recycled. Percentages of all components in T2 stream, Recycle stream, ECS input stream remains is same. Following is tabulated the ECS INPUT STREAM : COMPONENTS Kgmol/hr Mol% Kg/hr Wt% N2 169.0765 87.26417 4734.143 87.28446 O2 14.48942 7.478312 463.6614 8.548629 CO 2.131467 1.10098 59.68109 1.100354 DME 0.655507 0.338332 30.15332 0.555943 CH2O 0.02079 0.01073 0.623713 0.0115 CH3OH 0.19491 0.100597 6.237126 0.114995 H2O 7.183908 3.70777 129.3103 2.384124 TOTAL 193.7525 100 5423.81 100

RECYCLE STREAM: COMPONENTS Kgmol/hr Mol% Kg/hr Wt% N2 508.6225 87.26417 14241.51 87.28446 O2 43.58788 7.478312 1394.812 8.548629 CO 6.402479 1.10098 179.2694 1.100354 DME 1.971933 0.338332 90.7089 0.555943 CH2O 0.062543 0.01073 1.876287 0.0115 CH3OH 0.58634 0.100597 18.76287 0.114995 H2O 21.61104 3.70777 388.9986 2.384124 TOTAL 582.8573 100 16315.94 100

ECS OUTLET: In ECS system CO, HCHO, DME, CH3OH are converted to CO2. Following are the reactions to form CO2 on fixed catalyst bed of Platinum: 1)

CO + 1/2O2

CO2

2)

HCHO + O2

CO2 + H2O

3)

CH3OCH3 +3O2

CO2 + 3H2O

4)

CH3OH + 3/2O2

CO2 + 2H2O

However some CO still remains. Standard norm for CO is 50ppm. 0.16% of the CO in the ECS inlet goes in the ECS outlet, while rest all other compounds get 100% converted to CO2 by above reaction. This hot ECS outlet is used to heat dowtherm oil . Following is the composition of the ECS outlet stream: COMPONENTS N2 169.0765 O2 11.29901 CO 0.310004 H2O 9.56104 CO2 2.692671

Kgmol/hr Mol% Kg/hr Wt% 87.632 4734.143 87.75109 5.856250 361.5683 6.701956 0.160674 8.680114 0.160893 4.955466 172.0987 3.189986 1.395605 118.4775 2.196075

TOTAL

192.9393

100

5394.968

100

Now the blower will discharge mixture of fresh air and recycle stream into the evaporator.

FRESH AIR COMPOSITION : As calculated earlier fresh air amount was 220.7141Kgmol/hr. Following is the composition of fresh air : COMPONENTS Kgmol/hr Mol% Kg/hr Wt% N2 170.612 77.3 4777.137 75.75248 O2 44.80497 20.3 1433.759 22.73555 H2O 5.297139 2.4 95.34851 1.51197 TOTAL 220.7141 100 6306.244 100 NEW BLOWER DISCHARGE : So the new blower discharge will have the following tabulated composition: COMPONENTS Kgmol/hr Mol % Kg/hr Wt% N2 679.2375 84.52834 19018.65 84.07302 O2 88.39285 11.00013 2828.571 12.50346 CO 6.402479 0.796762 179.2694 0.792445 DME 1.971933 0.245399 90.7089 0.400971 CH2O 0.062543 0.007783 2.001373 0.008847 CH3OH 0.58634 0.072968 18.76287 0.08294 H2O 26.90817 3.348613 484.3471 2.141015 TOTAL 803.5619 100 22622.31 100 This is the complete material balance for the formaldehyde plant in phase 2.

PRECAUTIONS AND SAFETY FACTORS:

Formaldehyde is highly toxic by inhalation and oral intake. The vapors are very much irritating to the eye and upper respiratory system. Though liquid is not highly irritating to skin, it can cause severe eye burns. Topical application may produce irritant dermatitis ingestion may cause severe abdominal pain, acidosis, vertigo, coma, death High concentrations are intolerabl. Explosive limit of formaldehyde in air is: LEL: 7% HEL 73% So proper precautions need to be taken while working on the formaldehyde plant. Safety equipments such as gloves, mask, apron, helmet, safety goggles, shoes, etc. must be used while working on plant. O2 control : Control of O2 concentration is essential. If methanol concentration in the gas to the reactor is below 7 vol%, then no pressure surge will occur, regardless of O2 concentration. However, when the methanol concentration is above 7 vol %, the O2 concentration must be below 13vol% to avoid the risk of an explosion. Because it forms explosive mixture in such cases. The plant has been equipped with rupture disc which gets open automatically in case of high pressure to avoid explosion. Also majority of the part of the stack gas is recycled which makes sure the oxygen concentration is well below 13% to avoid explosive mixture. Fire control : There is always a certain risk at elevated temperatures at the reactor top or at bottom. The plant has to be shut down in case of too high temperatures. As both methanol and the gas are stopped by SS-AB, any fire will extinguish itself. In the unlikely event that the fire does not cease, there is a nitrogen system connected to the reactor top of purging. FUTURE PERSPECTIVES : HOC holds very good reputation of being one of the greats in their field. The past years of company has been full of glory. Once a time, the company was one of the leading manufacturer of basic chemical products. However, the tradition has shown reverse trend these days. Due to immense competition from private sector & improper management strategy, the company is finding difficult to hold it’s status of being great in the market. No question in the world can be unanswered. The company need to be more reluctant, professional in attitude & have to take some tough decisions. Plants are still in good condition which can give product of high purity. The proper marketing strategy is must for any firm, if it has to remain intact in the global market. The working efficiency of workers as well as the higher officials needs to be improved. Well, the future of HOC is in the hand of HOC’ians.

REFERENCES : 1. PERRY’S HANDBOOK 2. PHYSICAL PROPERTIES BY CARL L .YAWS 3. LANGE’S HANDBOOK OF CHEMISTRY-TATA MCGRAW HILL 4. PROCESS HEAT TRANSFER BY DONALD Q. KERN

ACKNOWLEDGEMENTS We would like to express our sincere thanks to Dr. B.N.THORAT, UICT for providing us the platform to do the Inplant Training in HOC,Rasayani without which this project would not have been completed successfully. We would also like to express our since thanks to Mr.A.M.SATHE, HOC for his guidance for carrying out this project. We were really honored for the keen interest he took at each and every step of this work. We would like to express our deepest gratitude for his encouragement and confidence he showed in us while carrying out this project without which this work would have not been completed. We also like to thank Mr. M.S.Patil, for the efforts he has taken to help & guide us. We would also like to thank Mr. Jirimali and Mr.Virkar for the support they had given & faith they have shown in us.

INDEX Sr. No. Contents Pg. No. 1. Introduction to Company 1.1 Company background 3 1.2 Features of the company 2. Waste heat boiler design 3. Vaporizer design 13 4. Pressure drop calculations 5. Formaldehyde plant 5.1 Formaldehyde-useful industrial product 18 5.2 Introduction 5.3 Process flow sheet 5.4 Plant- functional description 5.5 Equipments used

5 8 16

19 20 21 24

5.6 5.7 5.8 5.9 5.10 6.

Product sprcification & storage Operational features & critical parameters Material balance Precautions & safety factors Future perspectives

30 31 34 42 43

References

44

INTRODUCTION COMPANY BACKGROUND : “HINDUSTAN ORGANIC CHEMICAL LTD.” A leader in Indian chemical industry for over three elected is further expanding its horizons in near future. Earlier company has to depend upon the imports for its vital organic chemical needs till the government with a view to making the company self reliant in this field set up HOC in 1960. Making a beginning as a small chemical unit HOC is today a multi technology, multi-unit company with three fast growing units. HOC has following manufacturing units:The main organic chemical complex at Rasayani in Raigad District (Maharastra) The phenol complex at kochi (Kerala) The poly tetra Flurothylene at Hyderabad (Andhra Pradesh) Initiating an era in basic chemical intermediates. Incorporated at rasayani, a backward area in Maharastra, HOC’s first plant started production in 1970. Between 1970 and 1974 a total of twelve plants were commissioned. Together they produce a large number of products that serve a wide spectrum of industries, ranging from pharmaceuticals to defense and space. After stabilization of the first phase plant in the sixth plan period (1980-85), a number of expansion and diversification plants were launched at Rasayani. Expansion phase included doubling of Hydrogen, Aniline, Nitro Benzene and Nitro Toluene and substantial expansion of Nitroclorobenzene. HOCL was established on 12th Dec.1960 by the Government of India, with the view of making the country self-sufficient in the filed of organic chemical manufacture. Initiating an era in basic chemical complex is a leader in Indian chemical industries manufacturing a wide range of high quality basic organic chemical which are required for variety of chemical and pharmaceutical product such as drugs, medical, dyes, plastics, resins, paints, textile, and explosive. The company has a continuous manufacturing process and works for 24hrs. A day in 3 shifts in all, around 22 plants are functioning at Rasayani. HOC has its head office situated at Mumbai. The company provides various facilities to its employees like canteen, transport, residential quarter, library and hospital, etc.

FEATURES OF THE COMPANY : Training Centre : HOC has as well-quipped training center, which arranges regular courses for developing skills of employee at all, level. Periodic in house seminars are held, workshop are conducted for employees. Which help them sharpen their skills. Safety department : In everything HOC does, safety of its employees is a prime consideration. This concern is manifest is a multitude of ways. Safety department provide Safety devices to the workers and trains them to work Safety and continuously. Fire department : The fire officer train the personnel to deal with an emergency like fire etc. and teach them to make proper use of fire extinguishers and Safety equipments. Health center : The company health center is well equipped with all the medicines and has its own ambulances. There are qualified doctor in medicals center who examine the workers regularly during the routing medical check up.

Research & Development : In order to diversify, lower the costs and increase existing capacities, HOC’s R & D efforts are being directed toward assimilation and adaptation of most modern international technologies and development of new and improved processes and chemicals. Scale-up studies are being undertaken through pilot plants, while facilities are being augmented for catalyst testing and sophisticated analysis.

In-house research apart, HOC’s R & D division collaborates with scientists from Universities, Institutes of technology and National Research Laboratories, involved in nation building projects. In house in the R & D department has led to the installation of pilot plant for production of cyclohexyl amine. The R& D department is pursuing it’s efforts in the development of noble metal catalyst for increased manufacture of CHA. By recovering resorcinol- a value added chemical from meta amino phenol plant, due efforts of R & D department, HOC has won many prestigious award. Quality Control HOC is very conscious of maintaining a high quality of its products and for this purpose right from raw material through processing to finished product, through checking and stringent tests are carried out at every stage by experts in a modern wellequipped laboratory.

Quality control: HOC is very conscious of maintaining a high product, right from raw materials, to finished products, through checking and experts in a modern wellequipped laboratory carry out stringent test at every stage. Export : What began as an import substitution effort years ago is now an export activity that is steadily gaining momentum. The fact that HOC has generated self-sufficiency in chemicals in India is further complimented by its exports to countries like USA, France, UK, Japan, Germany and many others. Competitive pricing and high quality make HOC’s prospects excellent on the export scene. Today HOC stands as a winner of several awards for excellent export performance from CHEMEXCIL (Basic chemicals, pharmaceuticals and cosmetics export promotion council), an organization set up by the Government of India.

WASTE HEAT BOILER DESIGN :

In 1-2 Shell and Tube heat exchanger (WHB), on shell side water flows at 2000 Kg/hr while on tube side HTM oil flows. We have to calculate the steam generation rate. HTM OIL: Inlet temperature of HTM oil = 173oC Outlet temperature of HTM oil = 160oC WATER: Inlet temperature of water = 80oC Outlet temperature of steam = 150oC Following are the physical properties of the concerned fluids: PROPERTIES HTM OIL Ρ, Kg/m3 1000 1000 Cp, Kcal/KgK 0.76 1 µ, Poise 0.3x10-3 K, W/Mk 0.1 0.6

WATER STEAM 1.2 0.47 10-3 1.42x10-4 0.02836

TUBES: Number of tubes = 178 Outer diameter of 1 tube = 1.25in. Thickness = 10BWG Inner diameter of tube = 0.982in. Total heat transfer area for heat exchanger = 117.45m2 Assuming overall heat transfer coefficient, Ud = 240W/m2K Log mean temperature difference is, ∆Tlm = ((173-150)-(160-80))/ln ((173-150)/ (160-80)) = 45.72oC

So, total heat duty will be, Q = Ud A ∆Tlm = 240 x 117.45 x 45.72 Q = 1288755.36 Watts Now, Total heat duty = Specific heat given by HTM oil

Q

= mcp∆Tlm = 1288755.36 = m x 0.76 x (173-160)

HTM oil mass flow rate, m = 24.8 Kg/s = 89,280Kg/hr. HEAT TRANSFER COEFFICIENTS: On tube side: Area of cross section of one tube, a = Π/4x (0.982 x 0.0254)2 = 4.885x 10-4 m2 Velocity, V = volumetric flow rate /area = 24.8 x 2 / (1000 x 178 x 4.885 x 10-4) Number of passes = 2 and number of tubes = 178 V = 0.57m/s. Reynolds number, Re = DVρ/ µ = (0.0249 x 0.57 x 1000)/ (0.3 x 10-3) = 47345

Prandtl number,

Pr = Cp µ/K =

0.76 x 4184/0.1

=

7.026

Nusselt number, Nu = 0.023 Re0.8 Pr0.33 = 0.023 x 473450.8 x 7.0260.33 Since,

Nu = hd/k

So, hd/k = 175.84 h

= 706.211

hio

= 554.8W/m2K …………. ( hio = h x ID/OD)

So, heat transfer coefficient on tube side, hio = 554.8W/ m2K Shell side: Square Pitch = 1.5in. Shell area = 1.5” x 1.5” = 2.25sq.in. Tube area = Π/4 x 1.252 = 1.227sq.in. Total tube area = 178 x Π/4 x 1.252 = 218.44sq.in. Shell area = (2.25/1.227)x178 = 326.41sq.in. 326.41 = Π/4x D2s Ds = 20.39in. = 0.518m Baffle spacing = 0.5 x Ds = 0.5 x 20.39 = 10.195in. = 0.258m Equivalent diameter, Deq = 4xflow area/wetted parameter = 4 x (1.52 - Π/4 x 1.252)/ (Π x 1.25) = 1.04 in. Flow area = baffle spacing x clearance x shell ID/pitch = 10.195 x (1.5 - 1.25) x 20.39/1.5 = 0.0224m2 Velocity, V = Volumetric flow rate / flow area = 2000/ (3600 x 1000 x 0.0224)

= 0.0248m/s Reynolds number, Re = DVρ/ µ = 0.0264 x 0.0248 x 1000/10-3 = 654.72 Prandtl number, Pr = Cp µ/K = 1 x 4184 x 10-3/0.6 =7 Nusselt number, Nu = 0.36 Re0.55 Pr0.33 = 0.36 x 654.720.55 x 70.33 hd/k = 89.17 ho = 2026.64 W/ m2K Heat transfer coefficient on shell side, ho = 2026.64 W/ m2K OVERALL HEAT TRANSFER COEFFCIENT: Overall clean heat transfer coefficient (Uc), 1/Uc = 1/ hio + 1/ ho = 1/554.8 + 1/2026.64 = 451.34 W/ m2K Now dirt factor, Rd = 1.785x10-3K/W m2 So, Overall heat transfer coefficient (Ud), 1/ Ud = 1/ Uc + Rd = 1/451.34 + 1.785x10-3 Ud = 242 W/ m2K So, calculated Ud is fairly matching with the assumed value. Now, Total heat duty = (mcp∆T) water + mλ + (mcp∆T) steam

1288755.36 = m x 4184 x (100-80) + m x540x4184 + m x 1967.63x (150-100) m = 0.5278Kg/s = 1900 Kg/hr. So, the required steam generation rate is 1900Kg/hr.

VAPORIZER DESIGN : VAPORIZER :

To check the design for vaporizer : There are 3 zones in the vaporizer. 1.

preheating zone

2.

flashing zone

3.

superheating zone

A) Let UD= 25 w/m2k So, Q = UD A ΔTLM = (m CP ΔT)H2 = 446.42 x 3.46 x 4184 x 4 Q = 7180.74 W 7180.7 = 25 x A x 43.5 A = 6.6 m2…. required area. Provided area = 92.787 m2 B) m cp (160-T)H2

= m λNB

446.2 x 3.46 x 4184 x (160-T) = 2000 x 334720 / 3600 => (160-T) = 0.02877 T = 159.97 oC.

C) Q = m cp (160-T) H2 + m cp (160-T)NB

= 446.42 x 3.46 x 4184 x 0.02872 + 2000 x 3.46 x 4184 x 0.02877/ 3600 Q = 1094.3 W Area provided = 0.6823 x 46 = 31.39 m2 Let, UD = 25 w/m2k & we calculate ΔTLM = 41.49 1094.3 = 25 x A x41.49 A = 1.055 m2 Zone Area calculated, m2 Actual area, m2 Preheating 6.6 92.787 Superheating 1.055 31.39

PRESSURE DROP CALCULATIONS : Calculations of pressure drop across 90o bend having 80 mm diameter and with air flow rate 5000Nm3/hr at 9Kg/cm2 and 50oC. Assumptions : Ideal gas laws such as Boyle’s law are considered to be valid for given air at NTP Data: 1. ρair = 1.2 Kg/m3 2. Head loss coefficient for 90o bend (K) = 1

Solution : 22.4 dm3 of gas at NTP = 1gmol 5000Nm3/hr of gas at NTP = X gmol X = 223214.29 gmol/hr = 6473.2147 Kg/hr Air flow rate at NTP (25oC & 1Kg/cm2 pre.) = 6473.2147 Kg/hr By ideal gas law, V1/T1 = V2/T2 V2 = V1 x T2/T1 V2 = 1.2 x (273.16 + 50) / (273.16+25) = 1.3006 m3 for 1 kg of gas at 50oC

From Boyle’s law, P1V1 = P2V2 V2 = P1V1 = 1 x 1.3006/9 = 0.1445 m3 for 1Kg gas at 50oC and 9Kg/cm2 Now, Density of air at 50oC and 9Kg/cm2, ρair =1/V2 = 6.9204 Kg/m3 6473.2147 Kg of gas = 6473.2147/6.9204 = 935.444 m3 Area of cross section of pipe, A=

d2/4 = 5.0265 x 10-3m2

Velocity, V = volumetric flow rate / A = 935.44/(5.0265 x 10-3 x 1000) = 51.6917 m/s Pressure drop (ΔP), ΔP = ½ ρairV2 K = ½ x 6.9204 x (51.6917)2

x1

= 9245.76Pa ΔP = 0.09248 kg/cm2 Therefore, the pressure drop across 90o bend = 0.09248 kg/cm2 FORMALDEHYDE FORMALDEHYDE – USEFUL INDUSTRIAL PRODUCT: 1. Formaldehyde is useful chemical employed in the manufacture of many industrial product and consumer articles. 2. Formaldehyde is used in the manufacture of phenolic resins, artificial silk and cellulose esters, dyes, organic chemicals etc. 3. Formaldehyde is used as agent for improving the fastness of dyes on fabrics. 4. A major application of Formaldehyde in the manufacture of crop protection and soil disinfections chemicals, fumigants, pharmaceuticals and explosives. 5. It is used for tanning and preserving hides, and for preserving and coagulation of rubber latex.

INTRODUCTION : The current plant - formaldehyde phase 2 produces a 37% water solution of formaldehyde by the vapor phase oxidation of methanol by air in presence of Iron Oxide-molybdenum oxide catalyst in a fixed bed tubular reactor at 320-400°c and scrubbing the gas by D.M. water to absorb HCHO gas(formalin gas to get 37% HCHO. The plant is designed to produce a maximum of 55% HCHO. Alternative ways :

Following are the two alternative ways of production of formaldehyde. 1. Silver catalyst process in which methanol is oxidized over a silver catalyst at the atmospheric pressure and 600-650°C. 2. From the Methane by, partial oxidation. But it was found that the process of production of formaldehyde by using Iron-molybdenum oxide catalyst was much more efficient. Hence this process was employed in the plant. Properties : 1. Nature :- colorless liquid with pungent odors. 2. Density :- 1.08-1.085 gm/cm³ (25°C) 3. Boiling point :- 96°C 4. Refractive index :- 1.3746 (20°C) 5. Flash point :- 60°C. 6. Miscible with water, alcohol and acetone. 7. Hazard : - Toxic by inhalation, skin and eye irritant, moderate fire risk. Raw materials : Methanol, air and caustic soda. Utilities : D.M water, cooling water, chilled water, instrument air, power supply. PROCESS FLOW SHEET :

PLANT - FUNCTIONAL DESCRIPTION: The process is accomplished by the oxidation of methanol on a metallic oxide catalyst, using a fixed-bed vapor-phase oxidation converter, according to formula: CH3OH + ½O2 CH2O + H2O ∆H= -159 KJ/mol A low ratio of methanol to air is used to maintain the desired oxidation atmosphere, and the heat of reaction is removed from the converter by boiling a liquid heat transfer medium (Dowtherm A or equivalent medium). The methanol content in air is maintained between about 4 and 9 % by volume. Such a high content can be used because part of stack gas from the plant is recycled, which decreases the oxygen concentration sufficiently to avoid explosive mixtures. The process gives a high yield on a single passage, and also very high conversion making the recovery of methanol from the final product unnecessary. The actual formaldehyde yield is in the range of 91-94% of the theoretical. The remainder of the methanol is accounted for by unreacted methanol, carbon monoxide, dimethyl ether and a negligible amount of formic acid. The air is supplied by two root type of blowers, here items C-4 A/B. Methanol to the plant is supplied by pump, P-1 and is injected into the air stream after the vaporizer tube bundle through a spray nozzle ring. The air is passed through the methanol vaporizer, E-1, after which the methanol is vaporized. The gas mixture temperature to the reactor is now about 120°C.

The oxidation of the methanol takes place in a fixed-bed reactor with 11878 stainless steel tubes of 21mm. The tubes are loaded with the metallic oxide catalyst to a specific depth. The bottom and the top sections of the tubes are filled with small inert rings to improve the heat transfer.The reactor tubes are surrounded by Dowtherm to remove part of the heat of reaction. The gas mixture entering the top of the catalyst tube is preheated by the boiling Dowtherm in the reactor shell, while passing through the upper inert rings in the catalyst tube. As the gas reaches the heated catalyst, the reaction starts and the temperature rises rapidly to a maximum. When the main part of the methanol has reacted, the temperature drops rapidly again and approaches the temperature of the boiling Dowtherm when the gas leaves the reactor tube. An additional layer of catalyst is loaded below the reactor tubes in the adiabatic bed. The reacted gases pass out of the reactor bottom and back to vaporizer again. On the shell side of the vaporizer the gases are cooled to a temperature of about 110°C, depending on the flow of methanol. The cooled gases then flow to the absorption tower. The absorption takes place in the two columns, T-1 & T-2. The first column consists of a spray section and above that two packed beds. The second column consists of 15 bubble cap trays. Formalin solution of any desired concentration up to 55% can be obtained. The heat of absorption is removed by heat exchanger, E-7 and through cooling water pumped through coils located below the liquid level on each tray. Water is fed into the top of the second absorber and flows counter-current to the gas flow at a desired rate, depending on the formaldehyde concentration of the final product. The reactor shell is filled with boiling Dowtherm in order to obtain the maximum heat transfer rate. The Dowtherm is circulated by thermo siphon circulation through the reactor shell and into the vapor separator, E-3. The Dowtherm vapors are separated from the liquid in the vapor separator from where the liquid flows back to the converter. The vapors are condensed in a tube-and-shell heat exchanger, E-2. During start-up, before the heat of reaction has given sufficient thermosiphon circulation; the Dowtherm is circulated by pump P-2, and preheated in the Dowtherm heater. The Dowtherm condenser is also operated as a steam boil

EQUIPMENTS USED : Following are the equipments used in the plant for the production of formaldehyde. Air blowers, items C-4 A,B : The air blowers, which supply the air for the oxidation process, are Roots type of blowers. The maximum delivery pressure is 88 mbar. The normal air flow is 19200 Nm³/hr, which is achieved with two blowers. The blowers are connected to electrical motors. Different air flows are achieved by changing the pulleys of the blowers. Vaporizer, item E-1 : The vaporizer used is a shell and tube heat exchanger. It works as a flash vaporizer. A flash vaporizer is used because it eliminates the fire hazard; the amount of methanol in the process area is very small. The gas is heated in the vaporizer and after the tube bundle the methanol is sprayed into the gas. Then the gas passed a pack section before it enters the reactor. This part of the vaporizer is equipped with a rupture disc. The temperature of the gas mixture leaving the vaporizer is about 120°C. The heat to vaporize the methanol is taken from the hot gases coming from the reactor. Reactor, item R-1 : The air-methanol mixture enters the top of the fixed-bed reactor, which is equipped with 11878 stainless steel tubes, 21.0 mm inside diameter and 1500 mm in length. The tubes are loaded with the metallic oxide catalyst to a specific depth. The bottom and the top parts of each length of tubes are filled with small inert rings. The purpose of these rings is to improve the heat transfer between the boiling Dowtherm and the incoming gas mixture as well as between the Dowtherm and the exit gas. In this way the gas mixture is preheated before it enters the reaction zone and the reacted gases are cooled rapidly upon leaving the catalyst zone. The reactor top is also equipped with two rupture discs, six of the reactor tubes are fitted with stainless steel thermocouple wells. Each one equipped with six thermocouples in fixed positions. Below the tubes in the reactor an additional layer of catalyst is loaded, the adiabatic bed. There is no cooling in this part; therefore the temperature of the gas leaving the bed is increased by approx. 10°C

Vapor separator, item E-3 : The Dowtherm vapor separator is cylindrical, vertical vessel, located besides the reactor. In the vessel the Dowtherm vapor is separated from the liquid as it is forced from the converter by the thermo siphon circulation. The Dowtherm vapor from the vapor separator is condensed in the waste heat boiler, which is located just above the vapor separator. The liquid Dowtherm in the vapor separator flows back into the converter and again into the vapor separator. The vapor separator is maintained about half-filled or somewhat less with liquid Dowtherm during operation, i.e. when the dowtherm is boiling. Condenser , item E-2 : The Dowtherm vapors from the vapor separator are condensed in a tube-and-shell heat exchanger, which is also operated as a boiler. The boiling water is kept on the shell side. The boiler feed water level in the condenser is controlled automatically by the control loop. Steam of pressure up to 22 Kg/cm² (g) can be produced. The condenser is equipped with a level glass for the boiler feed water level and two safety valves for the steam system. Absorption towers, items T-1, T-2 : The bottom section of the column T-1 contains 6 spray nozzles through which the product solution circulates. By means of these nozzles the walls of the bottom section are continuously sprayed with formalin. This is important in order to prevent precipitation of Para formaldehyde. All nozzles point upwards. The bottom section of the column is also equipped with a steam coil intended for heating primarily in case of an interruption in production. In addition, there is a level glass, a level controller, alarms for high and low levels and temperature indicators. Above the spray section there are two packed beds through which the formaldehyde solution is pumped by means of the circulation pumps. The formaldehyde solution, which is circulating over the upper packed bed, is cooled by an external plate heat exchanger, E-7. The second tower T-2 consists of 15 bubble cap trays, each containing 109 bubble caps. The trays are equipped with cooling coils for removing the heat of absorption. When producing formalin, process water is added to the upper tray in the column T-2 and the amount is controlled by the flow controller. At the top of the columns there are built-in drop separators for separating any entrainment carried along with the gas flow. In T-1this is only a prolonged pipe and in T-2 a demister of impingement type. A high pH value in the column contributes to more efficient absorption of formaldehyde. For this reason there is a piston pump for adding sodium hydroxide to the process water. To increase the chemical stability of the formaldehyde for storage, stabilizer is added in the outgoing product.

Chilled water passes through the cooling coils in the T-2 absorber and back to the chilled water unit. When having colder cooling water, the chilled water is completely or partly replaced with this. Absorption heat is also removed in heat-exchanger, E-7, where circulating formalin from the upper packed bed is cooled with cooling water. Dowtherm system : When the formaldehyde plant is not in operation, the Dowtherm stored is stored in a holding tank, E-6, and kept at a temperature of about 20-40°C, since dowtherm is solidified at a temperature of approximately 12oC. By storing the Dowtherm in this manner, it is possible to cool down the production equipment quickly, and there is no danger of freeing the Dowtherm in the system. When the formaldehyde plant is ready to go into operation, the Dowtherm is brought into the Dowtherm circulating system by means of dowtherm circulation pump. The Dowtherm in the separator is kept at low level in order to allow adequate room for expansion during the heat-up period. When the Dowtherm has reached the operating temperature, the Dowtherm level in the circulating system is adjusted, if necessary, to the proper operating level by adding or removing Dowtherm. During the operation of the plant, the Dowtherm vapor separator is maintained about half filled. The Dowtherm liquid in the separator exerts a hydrostatic head on the Dowtherm in the reactor R-1 and in the ECS heat recovery. In operation the Dowtherm vapor passes out from the top of the converter shell, R-1 and out from the top of the converter shell, and out from the top of the ECS heat recovery, sweeping Dowtherm droplets along with it, and enters the vapor separator. The pressure in the Dowtherm system can be regulated between 0 and 2 kg/cm² (g) by applying instrument air on the tube side of the Dowtherm condenser. The correct pressure is controlled by the controller. The Dowtherm condenser is equipped with a safety relief valve. During the start-up of the plant the heater located in the Dowtherm circulating system is turned on. When the Dowtherm has reached its operating temperature and the methanol feed has been started, the heater is turned off manually. Thermocouples are installed to check that there is no overheating of Dowtherm. N2 system : In case of a temperature surge, the methanol and blowers are shut off by the safety system. If the temperature still does not decrease, a fire-extinguishing system consisting of three N2 bottles must be manually opened. Emission Control System : The ECS consists of three different items. Item E-15 is a preheater for heating the gases from the absorber to the ignition temperature of the catalyst. Item E-18 is a vessel containing the platinium-catalyst. The catalyst bed which is supported on a screen has a height of approximately 60 mm. The reaction taking place is not cooled, therefore the gas temperature leaving the bed increases.The item E-17 is a tube heat exchanger where the hot gases leaving E-18 is cooled. On the tube side of the heat exchanger the hot gases heat the Dowtherm from the separator E-3.

Caustic pump : It has been found that a slight adjustment of the pH in the absorber by adding NaOH improves the absorption of the formaldehyde which is important when producing 55% formalin. When producing formalin, caustic pump can be used for adding NaOH to the process water. The feed rate to the absorption tower depends to some extends on the original pH of the water. However, the caustic forms in contact with formic acid sodium formate. This will increase the ash content in the product. Approximately 5 kg/h of a 5% NaOH-solution can be added which raise the pH at the top on the tower to appr. 9, to keep ash content in the product below 100 ppm. Recycle control valve : As the methanol oxidation to formaldehyde requires oxygen, fresh air must be continuously brought into the plant via the filter. Consequently, stack gas must be emitted via the ECS converter. By recycling about 75% of the exit gases from the absorber, only about 25% of the blower capacity is fresh air. The recycle control valve is positioned so that the oxygen analyzer during normal operation indicates 10.5-11.00 percent by volume of oxygen. PRODUCT SPECIFICATION : Description: - clear and colorless liquid with pungent odor. Concentration: - 37% + 0.5 Methanol content: - 0.5 – 0.8 % Specific gravity at 25/25°C: - 1.097 Acidity: - 0.05% max Iron (as Fe):- 2ppm max. Ash content: - 0.01%max STORAGE : The product Formaldehyde store in the stainless steel tanks at a temperature of 4749°C. With the decrease in temperature and increase in the concentration of aqueous HCHO solution tend to precipitate to Para formaldehyde. At high temperature, the tendency to formic acid increased. Hence the appropriate storage temperature must be maintained. Stabilizer solution methanol serves to inhibit polymer formation. Tank agitation and steam tracing is also provided for preventing Para formaldehyde formation.

OPERATIONAL FEATURES AND CRITICAL PARAMETERS : The plant has been equipped with an interlock system to protect personnel and the environment as well as to prevent damage to the plant itself. The interlock system controls the process either by shutting off methanol flows to reactor (safety system SWS-B) or airflow from blowers (safety system SS-A). The interlock system is activated if any- predetermined critical limit is reached on the parameters as in the following situations: Methanol flow to the vaporizer is an important control parameter. If there is a high alarm which is alerted at a methanol inlet of vapoarizer. In combination with O2, SS-B will be activated and methanol feed will be stopped. The valve is located very near the vaporizer to ensure that as litttle as possible methanol will enter the vaporizer. The vaporizer top, where vaporization occurs, has a rupture disc connected to safety AB, which stops air and methanol flow to reaction line.

The safety system AB activated in case of a too high discharge pressure is obtained from the blowers and hence the blowers and methanol feed are cut off. In case of a pressure surge the reactor; safety system AB to which the rupture disc is connected gets activated in order to shut down the methanol and air to reactor. In the tubular reactor, six of the tubes are fitted with stainless steel thermocouple wells, inside of which are fixed thermocouples. The highest temperature of per chosen thermocouples in each well will alarm if it exceeded the set limit. Safety system SS-D: In plant shut down stage, the dowtherm is stored in a tank where its temperature is maintained between 20-40°C (it solidifies at about 12°C approximately). An electric heater is used to heat the dowtherm about 100°C and hence it avoids water contamination in fresh dowtherm. This heater is connected with SS-D, which automatically shuts off heater incase of a high exit temperature. Oxygen Control: During operation, the O2 concentration of gas going to the reactor is kept constant, by an automatic controller at 11 vol%. This concentration means that approximately 1/3rd of fresh air and 2/3rd of recycle gas from absorber is fed to the reactor. Control of O2 concentration essential. If methanol concentration in the gas to the reactor is below 7 vol%, then no pressure surge will occur, regardless of O2 concentration. However, when the methanol concentration is above 7 vol %, the O2 concentration must be below 13vol% to avoid the risk of an explosion. HCHO Concentration control: A specific concentration profiles is achieved in the absorbers, depending on parameters such as water supply, temperature and the feed gas. If product concentration goes up it means the supply of water is insufficient and must be increased. If the HCHO concentration decreases, then either too much water is being fed or some of the cooling coils in the absorber are leaking. If decreasing the water flow at the top does not reverse the trend of down going concentration, then the coils are to be leak tested. Caustic soda (5%) is also added to the process water in order to achieve better absorption. The pH profile in the absorber is important. At a pH of 8.5, absorption is optional. Formaldehyde pumps and pipelines: All pumps in contact with formaldehyde are always to be drained when not in operation, and thus it assures that no Para formaldehyde formation occurs, which can damage the pumps. All piping in the circulation system for strong formaldehyde solution around the absorber is insulated and steam raced. The insulation is 50mm thick. These actions and control procedures assure that the plant will not produce any hazardous substances and will operate without any interruptions. Emergency stop : In the control panel there is a red key operated mushroom push button as emergency stop together with a push button with light (reset button). If the emergency stop has been pushed the light in the reset button turns off. To reset the system the key is used to release the emergency stop and thereafter the reset button is pushed in.

MATERIAL BALANCE : General process block diagram :

RECYCLE GAS

COMPOSITION OF AIR :

Blower Discharge i.e. Total air flow rate = 18000Nm3/hr And 1 gmol = 22.4dm3 Thus, 18000 Nm3/hr = 803.5714 Kgmol/hr COMPONENTS Kgmol/hr %MOL Kg/hr Wt% N2 677.7116 84.33744 18975.924 83.96472 O2 88.39286 11.0 2828.5714 12.51587 CO 6.402479 0.79675 179.26943 0.793232 DME 1.713954 0.21329 78.841864 0.34886 CH2O 0.062566 0.00779 1.8769821 0.008305 CH3OH 0.586567 0.073 18.770143 0.08304 H2O 28.70139 3.57173 516.62509 2.285964 TOTAL 803.5714 100 22599.879 100 METHANOL FEED: % CH3OH in mixed stream = (A*2240)/ ((32*B) + (22.4*A)) =7.5 Where, A= CH3OH flow rate in Kg/hr B= Air flow rate in Nm3/hr = 18000Nm3/hr Here we get, A = 1930Kg/hr Reactions taking place in Reactor: 92.5 % 1)

CH3OH + 1/2O2

CH2O + H2O 3.5 %

2)

CH3OH + O2

CO + 2H2O 1.5%

3)

CH3OH + CH3OH

4)

0.03% CH3OH + O2

5)

CH3OH

CH3OCH3 + H2O

CHOOH +H2O 2.47 %

INLET TO REACTOR:

CH3OH

Some CH3OH is coming from the blower and some is coming from CH3OH feed, so Total CH3OH in = 1935/32 + 803.5714*0.073/100 Input stream = 60.8995 Kgmol/hr Following are given the amount of CH3OH, O2 used and other compounds formed: In Reaction 1 , CH3OH used O2 used CH2O formed H2O formed In Reaction 2, CH3OH used O2 used CO formed H2O formed

= = = =

56.332Kgmol/hr 28.166Kgmol/hr 56.332Kgmol/hr 56.332Kgmol/hr

= = = =

2.13148Kgmol/hr 2.13148Kgmol/hr 2.13148Kgmol/hr 2.13148Kgmol/hr

In Reaction 3, CH3OH used = 1.82699Kgmol/hr H2O formed = 0.91349Kgmol/hr In Reaction 4, CH3OH used = 0.0182699Kgmol/hr H2O formed = 0.0182699Kgmol/hr In Reaction 5, CH3OH used = 1.50422Kgmol/hr

AT OUTLET OF REACTOR: Outlet of the reactor is used as a heating medium in the evaporator to evaporate methanol. Following is its composition: COMPONENTS Kgmol/hr Mol % Kg/hr Wt% N2 677.7116 75.71395 18975.92 77.26632 O2 58.0773 6.488397 1858.474 7.567348 CO 8.533947 0.953413 238.9505 0.972961 DME 2.62744 0.293538 120.8622 0.4921218 CH2O 56.3942 6.300361 1691.826 6.888791 CH3OH 1.504207 0.16805 48.13462 0.195995 H2O 90.22772 10.08024 1624.099 6.613019 CHOOH 0.01838 0.002053 0.84548 0.003443 TOTAL 895.0948 100 24559.12 100

This outlet stream of reactor is used for vaporizing CH3OH and in turn to reduce its temperature for better absorption in the two absorbers later. From the absorber we get the required product i.e. 37% Formaldehyde (wt %). From the outlet of reactor 2.5Kg/hr CH2O, 25Kg/hr CH3OH and whole N2, O2, CO and DME goes to T2 outlet thus, CH2O = 1689.326Kg/hr Thus for CH2O to be 37% total amount required (X) is, 1689.326 *100/X = 37 X = 4565.779Kg/hr Water added for absorption is 90.5% of amount of CH3OH feed. Water required to make product 37% by wt = 4565.779-(1689.326+ 23.13462+0.84548) Amount of water in the product = 2852.44 Kg/hr Remaining amount of H2O goes to the T2 stream along with N2, O2, DME, some amount of CH3OH and CH2O. FD PRODUCT OUTLET : COMPONENTS Kgmol/hr Mol% Kg/hr Wt% CH2O 56.31087 26.12778 1689.326 37 CH3OH 0.722957 0.335446 23.13462 0.5067 H2O 158.4689 73.52825 2852.44 62.47478 CHOOH 0.01838 0.008528 0.84548 0.018518 TOTAL 215.5211 100 4565.746 100 T2 OUTLET STREAM : COMPONENTS Kgmol/hr Mol% Kg/hr Wt% N2 677.7116 87. 26417 18975.92 87.25446 O2 58.0773 7.478312 1858.474 8.548629 CO 8.533947 1.098872 238.9505 1.099127 DME 2.62744 0.338322 120.8622 0.555943 CH2O 0.083333 0.01073 2.5 0.0115 CH3OH 0.78125 0.100597 25 0.114995 H2O 28.79494 3.707775 518.309 2.384124 TOTAL 776.6098 100 21740.02 100 T2 outlet stream gets divided into two streams which are as follows:

1. 2.

RECYCLE STREAM ECS INPUT STREAM

Amount of fresh air (X) required can be calculated as: (803.5714-X) x 7.478312 + X x 20.3 = 803.5714 x 11 X = 220.7141Kgmol/hr Thus, amount of recycle stream = 803.5714-220.7141 = 582.8573Kgmol/hr Amount of ECS stream

= T2 stream - recycle stream

= 776.6098 – 582.8573 = 193.7525Kgmol/hr EMISSION CONTROL SYSTEM (ECS) : At equilibrium stage, amount of CO generated in reactor system goes to the ECS system while the rest gets recycled. Percentages of all components in T2 stream, Recycle stream, ECS input stream remains is same. Following is tabulated the ECS INPUT STREAM : COMPONENTS Kgmol/hr Mol% Kg/hr Wt% N2 169.0765 87.26417 4734.143 87.28446 O2 14.48942 7.478312 463.6614 8.548629 CO 2.131467 1.10098 59.68109 1.100354 DME 0.655507 0.338332 30.15332 0.555943 CH2O 0.02079 0.01073 0.623713 0.0115 CH3OH 0.19491 0.100597 6.237126 0.114995 H2O 7.183908 3.70777 129.3103 2.384124 TOTAL 193.7525 100 5423.81 100

RECYCLE STREAM: COMPONENTS N2 508.6225 O2 43.58788 CO 6.402479 DME 1.971933 CH2O 0.062543

Kgmol/hr 87.26417 7.478312 1.10098 0.338332 0.01073

Mol% Kg/hr 14241.51 1394.812 179.2694 90.7089 1.876287

Wt% 87.28446 8.548629 1.100354 0.555943 0.0115

CH3OH 0.58634 0.100597 18.76287 0.114995 H2O 21.61104 3.70777 388.9986 2.384124 TOTAL 582.8573 100 16315.94 100

ECS OUTLET: In ECS system CO, HCHO, DME, CH3OH are converted to CO2. Following are the reactions to form CO2 on fixed catalyst bed of Platinum: 1)

CO + 1/2O2

CO2

2)

HCHO + O2

CO2 + H2O

3)

CH3OCH3 +3O2

CO2 + 3H2O

4)

CH3OH + 3/2O2

CO2 + 2H2O

However some CO still remains. Standard norm for CO is 50ppm. 0.16% of the CO in the ECS inlet goes in the ECS outlet, while rest all other compounds get 100% converted to CO2 by above reaction. This hot ECS outlet is used to heat dowtherm oil . Following is the composition of the ECS outlet stream: COMPONENTS Kgmol/hr Mol% Kg/hr Wt% N2 169.0765 87.632 4734.143 87.75109 O2 11.29901 5.856250 361.5683 6.701956 CO 0.310004 0.160674 8.680114 0.160893 H2O 9.56104 4.955466 172.0987 3.189986 CO2 2.692671 1.395605 118.4775 2.196075 TOTAL 192.9393 100 5394.968 100 Now the blower will discharge mixture of fresh air and recycle stream into the evaporator.

FRESH AIR COMPOSITION : As calculated earlier fresh air amount was 220.7141Kgmol/hr. Following is the composition of fresh air : COMPONENTS Kgmol/hr Mol% Kg/hr Wt% N2 170.612 77.3 4777.137 75.75248 O2 44.80497 20.3 1433.759 22.73555 H2O 5.297139 2.4 95.34851 1.51197 TOTAL 220.7141 100 6306.244 100 NEW BLOWER DISCHARGE : So the new blower discharge will have the following tabulated composition: COMPONENTS Kgmol/hr Mol % Kg/hr Wt% N2 679.2375 84.52834 19018.65 84.07302 O2 88.39285 11.00013 2828.571 12.50346 CO 6.402479 0.796762 179.2694 0.792445 DME 1.971933 0.245399 90.7089 0.400971 CH2O 0.062543 0.007783 2.001373 0.008847 CH3OH 0.58634 0.072968 18.76287 0.08294 H2O 26.90817 3.348613 484.3471 2.141015 TOTAL 803.5619 100 22622.31 100 This is the complete material balance for the formaldehyde plant in phase 2.

PRECAUTIONS AND SAFETY FACTORS: Formaldehyde is highly toxic by inhalation and oral intake. The vapors are very much irritating to the eye and upper respiratory system. Though liquid is not highly irritating to skin, it can cause severe eye burns. Topical application may produce irritant dermatitis ingestion may cause severe abdominal pain, acidosis, vertigo, coma, death High concentrations are intolerabl. Explosive limit of formaldehyde in air is: LEL: 7% HEL 73% So proper precautions need to be taken while working on the formaldehyde plant. Safety equipments such as gloves, mask, apron, helmet, safety goggles, shoes, etc. must be used while working on plant. O2 control :

Control of O2 concentration is essential. If methanol concentration in the gas to the reactor is below 7 vol%, then no pressure surge will occur, regardless of O2 concentration. However, when the methanol concentration is above 7 vol %, the O2 concentration must be below 13vol% to avoid the risk of an explosion. Because it forms explosive mixture in such cases. The plant has been equipped with rupture disc which gets open automatically in case of high pressure to avoid explosion. Also majority of the part of the stack gas is recycled which makes sure the oxygen concentration is well below 13% to avoid explosive mixture. Fire control : There is always a certain risk at elevated temperatures at the reactor top or at bottom. The plant has to be shut down in case of too high temperatures. As both methanol and the gas are stopped by SS-AB, any fire will extinguish itself. In the unlikely event that the fire does not cease, there is a nitrogen system connected to the reactor top of purging. FUTURE PERSPECTIVES : HOC holds very good reputation of being one of the greats in their field. The past years of company has been full of glory. Once a time, the company was one of the leading manufacturer of basic chemical products. However, the tradition has shown reverse trend these days. Due to immense competition from private sector & improper management strategy, the company is finding difficult to hold it’s status of being great in the market. No question in the world can be unanswered. The company need to be more reluctant, professional in attitude & have to take some tough decisions. Plants are still in good condition which can give product of high purity. The proper marketing strategy is must for any firm, if it has to remain intact in the global market. The working efficiency of workers as well as the higher officials needs to be improved. Well, the future of HOC is in the hand of HOC’ians.

REFERENCES : 1. PERRY’S HANDBOOK 2. PHYSICAL PROPERTIES BY CARL L .YAWS 3. LANGE’S HANDBOOK OF CHEMISTRY-TATA MCGRAW HILL 4. PROCESS HEAT TRANSFER BY DONALD Q. KERN