Manual Cagc-cag (1).docx

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TABLE OF CONTENTS 7

PRACTICAL EXERCISES MANUAL .................................................................................. 2 7.1

DESCRIPTION .............................................................................................................................. 2 7.1.1

Introduction ................................................................................................................................................ 2 7.1.2 Description of the unit ................................................................................................................................ 3 7.1.3 Description of the process ................................................................................................................. ......... 8 7.1.4 Practical possibilities ................................................................................................................................ 13 7.1.5 General specifications ...................................................................................................... ........................ 14 7.1.6 Dimensions and weight ....................................................................................................... ..................... 16 7.1.7 Required services...................................................................................................................................... 16 7.1.8 Required accessories (not included in the unit) ........................................................................................ 16

7.2

THEORY ...................................................................................................................................... 17

7.2.1 Drag flow and flooding velocity ............................................................................................................... 18 7.2.2 Overall mass balance ..................................................................................................................... ........... 20 7.2.3 Calculation of the overall mass transfer coefficient ................................................................................. 22

7.3

OPERATING MODE .................................................................................................................. 25

7.3.1 Valves operation ....................................................................................................................................... 25 7.3.2 Specific buttons of the CAG ................................................................................................. .................... 27 7.3.3 Operations required for the general handling of the unit .......................................................................... 28

7.4 7.4.1

7.5

MAIN INSTRUCTIONS, WARNINGS AND PRECAUTIONS ............................................. 55 Warnings and precautions ........................................................................................................................ 55

LABORATORY PRACTICAL EXERCISES ........................................................................... 57

7.5.1 Practical exercises 1: Determination and plot of drag and flooding flows ............................................... 57 7.5.2 Practical exercise 2: Analysis of gaseous currents using different methods ............................................. 63 7.5.3 Practical exercise 3: Analysis of water samples ....................................................................................... 68 7.5.4 Practical exercise 4: Determination of the mass transfer coefficient for a packed column ...................... 76 7.5.5 Practical exercise 5: Mass balance verification ........................................................................................ 88

7.6

ANNEXES .................................................................................................................................... 93 7.6.1 Assembly .................................................................................................................... .............................. 93 7.6.2 Filling the manometers ........................................................................................................................... 101 7.6.3 Frequent problems ...................................................................................................... ............................ 109

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7 PRACTICAL EXERCISES MANUAL 7.1 DESCRIPTION 7.1.1 Introduction Absorption is a basic operation of mass transfer that consists on the separation of some components of a gaseous mixture by contact with an adequate solvent. Mass transfer separation operations imply the contact of two immiscible phases. This contact can be intermittent, as it happens in plate columns, or continuous, as it happens in packed columns. Some processes that demonstrate the importance of absorption are: • The recovery of solvent vapors or natural gasoline from gaseous currents. • The treatment of gases in refineries. • The decontamination of industrial gases. The CAG or CAGC is a laboratory scale unit designed to study hydrodynamic and absorption processes in a packed column.

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7.1.2 Description of the unit CAGC unit

CAG unit

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5

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7

8

3

1 2

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11

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1. JE: 100 ml capacity syringe to take gaseous samples. 2. TU-U: ‘U’ shaped tube with two glass spheres where the solution with which the CO2 of a sample taken with the syringe (JE) will be retained is introduced. 3. COL: Column packed with Raschig rings. 4. VT-1: ‘T’ valve used to communicate line B and/or the syringe (JE) with the atmosphere. 5. VT-2: ‘T’ valve used to communicate line B with line C and/or the U shaped tube (TU-U). 6. VT-3: ‘T’ valve used to open or close the left hand branch of the M-1 and/or M-2 manometer with the upper or middle point of the column (COL). 7. VT-4: ‘T’ valve used to open or close the right hand branch of the M-1 and/or M-2 manometer with the upper or middle point of the column (COL). 8. VT-5: ‘T’ valve used to communicate line C with the upper or middle point of the column (COL) to take samples. 9. M-1: U shaped manometer to measure the pressure drop of the column bed (COL) between the upper and lower point or middle and lower point. 10.M-2: U shaped manometer to measure the pressure drop of the column bed (COL) between the upper and lower point or middle and lower point. 11.V-6: Valve that opens or closes the lower part of the U shaped tube (TU-U),

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which is the area where the solution used to retain the CO2 is introduced or removed. 12.V-7: Valve that opens or closes the lower part of the manometer (M-1), which is the area where the liquid used to measure pressure differences (H2O in our case) is introduced or removed. 13.V-8: Valve that opens or closes the lower part of the manometer (M-2), which is the area where the liquid used to measure pressure differences is introduced or removed. 14.VR-1: Valve that regulates the air flow that enters through the compressor (ACO-1). 15.VR-2: Valve that regulates the CO2 flow that enters through the cylinder that introduces that gas. 16.VR-3: Valve that regulates the water flow that enters through the water pump AB-1. 17.C-1: Flowmeter to indicate the air entering the lower part of the column (COL). 18.C-2: Flowmeter to indicate the flow of CO2 entering the lower part of the column (COL). 19.C-3: Flowmeter to indicate the flow of water entering the upper part of the column (COL). 20.S-CO2: Manual meter to measure CO2 in air currents. 21.V-10: Valve to open or close the measuring line of the CO2 meter for a

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sample at the inlet of the column (COL). This valve is optional in the CAG unit. 22. V-11: Valve to open or close the measuring line of the CO2 meter for a sample that correspond to the middle or upper part of the column COL. This valve is optional in the CAG unit.

6

1

5

3 2 4

Figure 1 – Lower part of the CAGC unit

1. V-9: Valve used to take samples of the water that reaches the lower part of the column (COL).

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2. ACO-1: Compressor used to supply the inlet air. 3. TAA: Water storage tank. 4. AB-1: Pump to supply the inlet water from the tank (TAA). 5. SC-3: Sensor to measure the inlet flow of water at the upper part of the column (COL). *Available in the CAGC unit. 6. VR-4: Valve that regulates the water flow that leaves through the lower part of the column (COL) towards the tank (TAA).

7.1.3 Description of the process The CAG or CAGC unit is a laboratory scale unit designed to study hydrodynamic and absorption processes in packed columns. These diagrams represent the system:

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7.1.3.1 Diagram of the CAGC

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7.1.3.2 Diagram of the CAG

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The system absorbs CO2 from a mixture with air in an aqueous solution that descends through the column. The unit consists of the following parts: - Packed column (COL). - Liquid circuit (water). - Gas circuit (air and CO2). - Measurement and analysis elements.  Liquid circuit The liquid, stored in a tank (TAA) made of PVC, is driven to the column with the aid of a magnetic drive centrifugal pump. The water flow that reaches the column is measured with a flowmeter (C-3) or with the flow sensor (SC-3) (if the unit is the CAGC version) and it is regulated with the valve (VR-3) and/or through the software actuator (if the unit is the CAGC version). The liquid is supplied to the column (COL) through its head with a glass diffuser. After crossing the column (COL), water passes to the storage tank (TAA) through a pipe with a hydraulic sealing to prevent leakages. There is a flow regulation valve (VR-4) and a sample taking valve (V-9).  Gases circuit Air is supplied by a blower (ACO-1). The gas (CO2 or ammonia) comes from a pressurized cylinder. The flow of both gases is measured by flow meters installed in line in the operation panel: C-1 for air and C-2 for CO2. The CAGC unit adds the possibility of measuring those flows through the software with the flow sensors (SC-1 for air and SC-2 for CO2). Both flows can be regulated with the valves

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VR-1 and VR2 respectively. Both gaseous currents are mixed and then introduced at the base of the column (COL) through a lateral inlet located below the bed level, so that the gaseous mixture is as homogeneous as possible. The air and CO2 will be expelled through the upper side of the column (COL) towards the atmosphere. For that reason, good ventilation is needed in the surroundings of the gas outlet. When starting the liquid circuit and gases circuit at the same time, after a while, water will have absorbed a certain amount of CO2 and the rest will be expelled to the atmosphere. Samples can be taken to be analyzed with solutions that allow to absorb the CO2, as the KOH solution.  Measurement and analysis devices The following devices are located in the operations panel: -

Two manometric tubes (M-1 and M-2) to determine the pressure drop

in the column. -

CO2 measurement device to determine the concentration of that gas in

the currents that come from the upper and central parts of the column. It consists of: • A 100 ml capacity glass syringe (JE) used to extract the precise amount of a gaseous sample for its analysis. • Two spherical glass vessels located at different height and interconnected by a tube (TU-U). An aqueous solution of KOH, in which the CO2 contained in the gas sample to be analyzed will be absorbed, is introduced in them (through the valve (V-6) with the aid of the syringe (JE)).

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• Three-ways valves (VT-1, VT-2, and VT-5) to direct the gaseous currents during the analysis process. • CO2 digital meter with reading via software. The CO2 concentration in the currents coming from the upper and lower parts of the column can be directly measured. This meter is optional for the CAG unit.

7.1.4 Practical possibilities 1. Determination of drag and flood flow rates in a packed column (COL). 2. Analysis of gaseous currents. 3. Analysis of water samples. 4. Demonstration of mass balances. 5. Determination of mean overall volumetric coefficients of mass transfer and the influence of the liquid flow rate on that coefficient.

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7.1.5 General specifications - COL: the column is a cylindrical tube made of glass with a length of 1400 mm and inner diameter of 75 mm. - Column packing (COL): glass Raschig rings 10x10 mm supported by a perforated plate made of nylon with a mesh that prevents the passage of the rings through the holes of the perforated plate. The specific area of packing per unit of volume of packing (m2/m3) for this type of rings is: a = 440 m2/m3. - TAA: Water tank of 40 liters of capacity. - AB-1: Water pump. o Maximum flow of 540 l/h with free outlet. o Maximum operating range: 2.7 l/min (70% of the flow meter). - ACO-1: Air compressor. o Maximum pressure: 1 bar. o Maximum flow rate: 6 m3/h. o Maximum operating range: 56 l/min (70% of the flow meter). - C-1: Air flow meter. o Operating range: 8-80 l/min. - C-2: CO2 flow meter. o Operating range: 2.4-24 l/min.

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- C-3: Water flow meter. o Operating range: 0.387-3.87 l/min. - M-1 and M-2: manometers 334 mm of height.

Particular specifications of the CAGC unit - SC-1: Sensor to measure the air flow. o Operating range: 5.2-80 l/min. - SC-2: Sensor to measure the flow of CO2. o Operating range: 2.4-24 l/min. - SC-3: Water flow sensor. o Operating range: 0.2-3.87 l/min. - SPD-1 and SPD-2: Differential pressure sensors. o Range: 0-1 psi. - SCO2: CO2 digital meter with reading via software (0-100%).

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7.1.6 Dimensions and weight o

Dimensions: 1000x740x2600 mm approx. o

Shipping volume: 2 m3. o

Weight: 150 kg. approx.

7.1.7 Required services - Electrical supply: 220V/50Hz single-phase. - Water supply to fill the tank.

7.1.8 Required accessories (not included in the unit) o CO2 gas cylinder with accurate pressure regulator. o KOH solute. o Ventilation conduit to the outside of the laboratory. o Drain tank to collect effluents. o General instrumentation liquids

for

the

titration

of

(phenolphthalein): beaker, scale, burette, dropping tube, etc. o Safety and prevention instrumentation: safety glasses, gloves, lab coat, etc.

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7.2 THEORY Gas absorption is a mass transfer operation whose objective is to separate one or more components (the solute) of a gaseous phase by using a liquid phase in which the components to be removed are soluble (the rest of components are insoluble). Components separation operations by mass transfer imply the contact of two unmixable phases. This contact is continuous in packed columns, although it can be intermittent if plate columns are used. Although there are other devices to achieve the contact between phases (atomizing chambers, gas bubblers, etc.), the most used ones in the absorption processes are the packed columns. Aspects such as the characteristics of the packing or the operation conditions are considered for the design of these columns. Thus, the knowledge of the different types of packing allows to select the most appropriate one in each case according to its specific area (m2 of packed area/m3 of occupied packed volume) and capacity (tolerable circulation velocity for both phases).

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7.2.1 Drag flow and flooding velocity One of the factors that influences when designing the diameter of a packed column is the flow rate of fluids, gas and liquid, that turns out to be tolerable through the packed bed. Thus, in a column that contains a specific packing, irrigated by a defined flow of liquid, the velocity of the gas has an upper limit, known as flooding velocity. The flooding velocity can be obtained from the relationship between the pressure drop throughout the packed bed and the flow of gas.

D' D C'

Bubblers Area C Point of Flooding

B' Load Area

B Load or Drag Point

A' Dry Filling A

log Gas Flow

Figure 2 – Pressure drop of the gas through the packing: drag and flooding velocities

Figure 3 shows the relationship, for different volumes of liquid, between the pressure drop and the volume of gas in packed beds with random pieces. For every constant flow of descending liquid, if the velocity of the gas is enough for the

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flow to be turbulent, the pressure drop of the gas is proportional to the square of its velocity (sections A-B and A’-B’ of the graph) for fluids inside piping. From point B on, when increasing the gas volume, (no matter the volume of liquid taken into account) the pressure drop starts being proportional to a power of the gas velocity higher than 2 and increasing continuously. Point B is the load or drag point, defined by a velocity of the gas and load or drag gas volume. When increasing the flow of gas above the load or drag value, a point in the curve is reached (C) in which it tends to be vertical. At that moment the liquid retention in the packing increases so much that it stops flowing down and all the gaps between packing pieces are filled with liquid. The gas bubbles in the core of the liquid, increasing its pressure drop extraordinarily. Point C is the flooding point. The gas velocity and flow that correspond to this point are called flooding velocity and flooding flow rate. The flooding phenomenon is demonstrated in the column by the accumulation or retrogression of the liquid inside, since the pressure drop in the gas is so high that the load of liquid is not enough to flow against that pressure.

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7.2.2 Overall mass balance The inlet and outlet flows of liquid (L) and gaseous mixture (G) are constant along a packed column. Therefore, the overall mass balance can be expressed as:

Where, Flow of gas that crosses the column (air + CO2).

(g/min)

Flow of water that crosses the column.

(g/min) (dimensionless)

Mole fraction of CO2 in the mixture (air + CO2) at the inlet of the column. (dimensionless) Mole fraction of CO2 in the mixture (air + CO2) at the outlet of the column. (dimensionless) Mole fraction of CO2 in the water at the inlet of the column. It is practically non-existent, water does not contain CO2.

Mole fraction of CO2 in the water at the outlet of the column.

(dimensionless)

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Figure 3 – Diagram representing the mass balance

Subscripts 1 and 2 are used to designate the currents at the inlet and outlet of the column respectively. Generally, the hypotheses below are taken into account in order to study the mass balance of a continuous and stationary absorption process in a packed column theoretically: - Only one solute is transferred from the gaseous state to the liquid state. - Both phases flow in countercurrent (the liquid descends and the gas ascends). - It is supposed that the pressure drop of the gas when crossing the column is negligible compared to the total pressure and that the balance is established in the interface instantaneously, that is to say, it does not offer resistance to the mass transfer.

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7.2.3 Calculation of the overall mass transfer coefficient The overall mass transfer coefficient is a characteristic parameter of mass transfer processes that indicate the ease with which one or more components of a phase in which the components to remove are soluble can be separated. The higher this coefficient, the better the mass transfer is. To calculate this coefficient several factors must be taken into account, among them the diameter and height of the packed column. The diameter of a packed column depends on: - Amount of gas and liquid - Properties of the gas and the liquid - Relationship between gas and liquid flows Nevertheless, the height of the column and, therefore, the total volume of packing, depend on: - Concentration variations to be achieved. - Mass transfer velocity per unit of volume of packing. Thus, height calculations are based on mass and energy scales balances and on the estimate of the driving forces and individual mass transfer coefficients during the liquid and gaseous phases (kl and kg). If the resistance of one of the two phases controls the transfer process, it will only be necessary to know the individual mass transfer coefficient through that phase, since it will practically coincide with the overall coefficient.

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and It can be demonstrated that the overall mass transfer coefficient through the liquid phase is obtained by this formula:

Where: Overall mass transfer coefficient through the liquid phase . Flow of CO2 absorbed by water

.

Specific area of packing per unit of volume of packing (m2/m3). Inner transverse area of the column (m2). Height of the column (m). Partial pressure at the inlet of the column given by:

Being

the mole fraction at the inlet of the column.

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Partial pressure at the outlet of the column given by:

Being

the mole fraction at the outlet of the column.

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7.3 OPERATING MODE 7.3.1 Valves operation  (VT-nº) Three-ways valves - The black spots indicate the open ways.

 (V-nº) Two-ways valves - Red arrows in the same direction of the flow: it runs freely. - Red arrows perpendicular to the direction of the flow: it is blocked.

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 (VR-nº) Regulation valves - They are opened by turning them in anticlockwise direction.

- They are closed by turning in clockwise direction.

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7.3.2 Specific buttons of the CAG

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7.3.3 Operations required for the general handling of the unit Before starting the practical exercises, it is essential to know how to perform the operations described below: 7.3.3.1 Fixing the flows 7.3.3.1.1 Air flow a.

Check that the air regulation valve (VR-1) is open and that the CO2 cylinder regulation valve (VR-2) is closed.

b.

Connect the air blower (ACO-1).

c.

Fix the desired value for the air flow with the valve (VR-1) and record the value of the flow using the flow meter (C-1) or from the value indicated by the sensor (SC1) if the unit is the computerized version.

d.

To calculate the volumetric flow from the flow meter:

*In the CAGC unit the volumetric flow is indicated by the sensor (SC1). e.

To calculate the mass flow under standard conditions (1 bar and 25ºC):

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7.3.3.1.2 CO2 and air flows (when activated at the same time) a.

Check that the air regulation valve (VR-1) is open.

b.

Activate the air blower (ACO-1).

c.

Connect the CO2 cylinder to the unit.

d.

Open the valve of the CO2 cylinder and adjust it to 1 bar.

e.

Regulate the air flow and the CO2 flow with the regulation valves (VR-1 and VR2).

f.

Record the value indicated by the flow meters (C-1 and C-2) or from the value indicated by the sensors (SC-1 and SC-2) if the unit is the computerized version.

Please note that as the air and the CO2 are connected in the same conduit, regulating one of the flows influences the other flow. For that reason they must be regulated when both gases are flowing. g.

To calculate the volumetric flows:

*In the CAGC unit, the volumetric flow is indicated by the sensors

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(SC-1 and SC-2) respectively. h.

To calculate the mass flow rates under standard conditions (1 bar and 25ºC):

i.

To calculate the molar flow rates:

j.

To calculate the initial mole fraction theoretically:

7.3.3.1.3 Water flow a.

Check that the water flow regulation valve (VR-3) and the water flow outlet regulation valve (VR-4) are fully open to allow water run freely.

b.

Activate the water pump (AB-1).

c.

Fix the desired value for the water flow with the valve (VR-3). It can also be

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regulated with the actuator (AB-1) of the interface in case the unit is the computerized version, CAGC. d.

Record the flow value using the flow meter (C-3) or from the value indicated by the sensor (SC-3) if the unit is the computerized version.

e.

To convert it into volumetric flow rate:

f.

To convert it into mass flow rate:

g.

Regulate the water level that goes down to the tank (TAA) through the valve (VR-4) so that the water level is between the MAX and the MIN shown in the figure, which represents the lower part of the packed column (COL). IMPORTANT: this step must be checked very frequently when the air and water flows are going to be modified. A water level variation influences the pressure measurement inside the column.

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7.5.2.3 Use of manometers As it can be observed the unit has two manometers (M-1 and M-2) to measure the pressure drop inside the column (COL). In the CAGC unit, apart from these manometers, there are pressure sensors (SPD-1 and SPD-2) that indicate the pressure along the column directly (COL).

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7.3.3.1.4 Manometer (M-1) Valves must be arranged in the position shown in the figure when using this manometer:

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7.3.3.1.5 Manometer (M-2) Valves must be arranged in the position shown in the figure when using this manometer:

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Valve VT-5 is used to determine if the pressure drop is measured along the entire column or only in half of the column:  Position of VT-5 to measure the pressure in the MIDDLE of the column:

 Position of VT-5 to measure the pressure in the ENTIRE column:

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7.3.3.2 Analysis of air flow samples 7.3.3.2.1 Theoretical method 1.

Fix the air and CO2 flow according to the method explained in the operating mode section when both flow rates must be operated at the same time and record the flow rates:

2.

Calculate the volumetric concentration of CO2 in the sample theoretically:

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7.3.3.2.2 Analytical method 7.3.3.2.2.1 Solution preparation

a.

Prepare a 5% KOH solution by pouring 50 grams of KOH in a beaker of 1 L capacity (add distilled water till the mark). This amount of solution will serve to analyze at least 8 gaseous samples.

b.

Place the beaker below the valve (V-6) with the tube that leaves from this valve inside the beaker.

5% KOH solution

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7.3.3.2.2.2 Introduction of the KOH solution in the U shaped tube (TU-U) with two glass spheres

a.

Check that the right hand branch of the U shaped tube (TU-U) is fully closed by its top (no air can enter or leave through it during the practical exercise).

b.

Place the valves (VT-1 and VT-2) as shown in the figure:

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c.

Pull the plunger of the syringe (JE) upwards to expel the air located inside to the atmosphere.

d.

Place the valves (VT-1 and V-6) as shown in the figure:

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e. Push the plunger of the syringe (JE) down (it can be observed how the KOH solution ascends from the beaker by suction through the left hand branch of the U shaped tube (TU-U)). Rise the solution up to height between 70 and 100 mm (observe the measurement in the scale of the left hand branch).

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NOTE: It may occur that the solution does not reach the required level with only one full stroke of the syringe’s plunger (JE). Please, continue with next step to reach that level. f.

Close the valve (V-6) and arrange the valve (VT-1) as shown in the figure:

g.

Repeat the steps 'c', 'd', 'e', 'f' till the KOH solution reaches a height between 70 and 100 mm in the scale located in the left hand branch of the U shaped tube (TU-U).

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h. Communicate the left hand branch of the U shaped tube (TU-U) that contains the solution with the atmosphere so that pressures inside the tubes reach the atmospheric pressure (it can be observed that a small part of solution passes to the right hand branch of the U shaped tube (TU-U)). For that purpose, the valve (VT-1) must communicate lines A and B.

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7.3.3.2.2.3 Taking a gaseous sample from the packed column

a.

Connect the blower (AS-1) and let the air flow along the packed column (COL) during a few minutes. Meanwhile:

b.

Position the valve (VT-1) as shown in the figure and push the plunger of the syringe (JE) to expel the air inside to the atmosphere.

c.

Position the valves (VT-1, VT-2, VT-3 and VT-4) as shown in the figure:

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d.

Arrange the valve (VT-5) to take samples from the middle or upper part of the column:  Position of VT-5 to take samples from the MIDDLE of the column:

 Position of VT-5 to take samples from the UPPER part of the column:

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e.

Pull the plunger towards the end of the syringe (JE).

f.

Repeat the steps 'b', 'c', 'd', 'e' at least three times to obtain a representative sample (please note that the first times only the air inside the tubes is taken, so the sample will be representative after performing these steps several times).

g.

Place the valve (VT-2) as shown in the figure:

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h.

Record the volume of the chosen sample:

i.

Record the level of the solution in the left hand branch of the U shaped tube (TUU):

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7.3.3.2.2.4 Start the reaction between the CO2 and the KOH

a.

Push the plunger of the syringe (JE) slowly to introduce the gas sample in the KOH solution vessel (it can be observed that the absorbing liquid is displaced to the second vessel, and when stopping to push the plunger, the liquid goes back to the left hand branch of the U shaped tube (TU-U)). Add the mixture slowly down to the end of the syringe (JE). IMPORTANT: Do not introduce all the sample in one go to prevent forcing the system and causing leaks.

b.

When stopping to push the plunger of the syringe (JE) it can be observed that it does not return to the initial position (100 ml if that was the sample taken for ), it remains above the initial value. It is due to the fact that part of the CO2 of

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the chosen sample has been absorbed by the KOH solution located inside the U shaped tube (TU-U).

c.

To see how much has been absorbed by the solution, pull the plunger VERY SLOWLY until it indicates the initial level of the U shaped tube (TU-U), that is to say, level recorded in the previous section (Taking a gaseous sample).

d.

Keep the liquid from the left hand branch of the U shaped tube (TU-U) to that level of

and record the new volume indicated by the plunger of the syringe:

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e. Repeat the steps 'a', 'b', 'c' and 'd' till the volume

starts to be repeated. If it is not

repeated refer to the section MAIN INTRUCTIONS, WARNINGS AND PRECAUTIONS.

7.3.3.2.2.5 Calculation of the CO2 concentration

1. Once the reaction is produced the volume of CO2 from the sample that has been absorbed by the KOH solution is calculated:

2. To calculate the concentration:

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7.3.3.2.3 CO2 meter (optional accessory for the CAG unit) 1. Arrange the valves (VT-2, VT-3, VT-4, V-10, V-11, VT-5) as shown in the figure:

V-11

V-10

2. Connect the CO2 meter.

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3. Position the valve (VT-5) to measure the CO2 concentration in the intermediate or upper part of the column (COL) and open the V-11 valve. The CO2 concentration may also be measured at the inlet of the column by opening the V-10 valve: MIDDLE part

UPPER part

V-11

V-11 V-10

V-10

4. Wait till the measurement of the meter is stabilized (when it does not change more than 1%). 5. Record the measurement of the meter:

6. Switch off the meter.

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7. Close the V-10 and V-11 valves if the meter is not going to be used again. 8. Disconnect the hose of the meter. 7.3.3.2.4 Conversion of the CO2 concentration into different units a.

Mass concentration is obtained:

b.

Molar concentration is calculated:

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7.3.3.3 Analysis of water samples 7.3.3.3.1 Preparation of an acid-base titration a.

Prepare a 0.02M NaOH solution. For that purpose dilute 0.32 g of NaOH in 400 ml of water.

b.

Refill the burette with a certain amount of the previously prepared solution. Record the initial volume of the burette:

c.

Pour the water sample to be analyzed in an Erlenmeyer flask of 100 ml.

d.

Add 10 drops of phenolphthalein indicator. If the sample turns pink, there is no CO2. If the sample remains colorless, add drop by drop the NaOH solution contained in the burette.

e.

When the sample turns pink and remains pink, close the stopcock of the burette and record the new volume of the burette:

f.

Calculate the volume of NaOH that has reacted:

g.

Note down and adjust the reaction that takes place:

h.

Calculate the CO2 in the water

concentration of sample: Volume of the NaOH solution Concentration of the used solution of NaOH

The molar concentration of CO2 in the sample will be:

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As the concentration of CO2 is very small, it is assumed that the density of the sample is the same than the density of the solvent or water. i.

Calculate the mole fraction of the sample:

j.

All the analysis must be done three times.

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7.4 MAIN INSTRUCTIONS, WARNINGS AND PRECAUTIONS  Check that there are no leaks. Apply some grease to all the areas prone to suffering leaks: o Plunger of the syringe o Valves o Connections of tubes with hoses  Introduce the gas sample with the syringe (JE) in several strokes.  First, fix the water flow and let it run for one minute. Then, fix the air flow (for the flooding practical exercise).  The software that corresponds to the CO2 meter must be installed in the CAGC unit if the user wants to use that meter. The software is included in the CD of the unit. 7.4.1 Warnings and precautions - Prevent the KOH solution from reaching a level in the U shaped tube (TU-U) very close to the end of the scale, otherwise a certain amount of solution could pass to the conduits of the gas samples taking lines and obstruct them.

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-

When the CO2 meter is NOT going to be used, the V-10 and

V-11 valves have to isolate the inlet to that sensor if this accessory or

V-10

the CAGC unit has been purchased. It is also recommended to V-11 disconnect the meter from the hose. And on the contrary, when this accessory is going to be used, the samples inlet valve must be fully open because the operation of the meter is based on aspirating and analyzing air samples. Likewise, the outlet orifice that is not connected to any hose must be open to the atmosphere.

-

Use always the CO2 meter with the suitable safety measures,

that is to say, water trap, particles filter and humidity filter.

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7.5 LABORATORY PRACTICAL EXERCISES 7.5.1 Practical exercises 1: Determination and plot of drag and flooding flows 7.5.1.1 Objective To determine the conditions under which the column drag and flooding process is generated and to plot the influence of the air and water flow rates variation on the pressure inside the column. 7.5.1.2 Required material - CAG or CAGC unit 7.5.1.3 Experimental procedure 1. Connect the water pump (AB-1). 2. Fix the water flow following the method described in the operating mode section. It is recommended to start with low water flow rates, as for example 30%. 3. Record the flow rate:

4. Activate the air blower (ACO-1). 5. Fix the air flow up to 10%, according to the method described in the

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operating mode section, to start with the minimum flow and be able to increase it gradually afterwards. To know the amount of air the user is working with, observe the flowmeter (C-1).

*In the CAGC unit the value of the circulating flow of air is given by the sensor (SC-1). 6. Wait until the steady state is reached (pressure does not change with time). 7. Record the pressure drop suffered by the gas when crossing the column. This value is obtained from the manometers of the panel (M-1 and/or M-2) (see the operating method in the operating mode section):

*In the CAGC unit the pressure is indicated by the sensors: (SPD1) for the entire column or (SPD-2) for the pressure of the lower half of the column. 8. For every flow of liquid fixed, the pressure drop that correspond to different air flow rates are measured (refer to the working sheet). 9. The natural logarithm for each flow rate and pressure drop recorded before. 10.The logarithm of the pressure drop suffered by the gas when crossing

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the column is plotted versus the gas flow rate logarithm. Thus, the loading and flooding flows can be identified. 11.Repeat all the steps again when modifying the water flow rate. 12.EDIBON recommends some pre-established water and air flow rates, which can be observed in Table 1 from the following section.

IMPORTANT:  When the flooding starts, it is observed how the column (COL) is being filled with water and the level rises gradually. Please, do not allow the water level inside the column (COL) obstruct the orifices that communicate with the manometers (M-1 and M-2) and sensors (SPD-1 and SPD-2), since they could give wrong values. If they were eventually obstructed, stop the water pump (AB1) and open the regulation valve (VR-4) up to the maximum by turning it in anticlockwise direction.  Please, take into account that high pressures will be reached for the flow rates that generate the flooding. For that reason, use only the manometer (M-1 or M2) with a liquid denser than water (the procedure to refill and discharge these manometers is indicated in the annex).

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7.5.1.4 Working sheet Student: ________

Year: __________

Table 1: Calculation of the drag and flooding flow rates

10 20 30 40 50 60 70

10 20 30 40 50 60 70

10 20 30 40 50 60 70

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7.5.1.4 Working sheet Student: ________

Year: __________

Graph 1: Plot of the gas pressure drops through the packing: Drag and flooding velocities.

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7.5.1.4 Working sheet Student: ________

Year: __________

Questions: 1. What occurs when the air flow rate is increased but the water flow rate is the same?

2. What occurs when the water flow rate is increased?

3. Identify the different sections of each curve and explain what occurs in each one.

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7.5.2 Practical exercise 2: Analysis of gaseous currents using different methods 7.5.2.1 Objective To analyze the amount of CO2 from a gaseous current using a solution of KOH. The method employed is based on the reduction of volume generated in a gaseous mixture when the CO2 disappears by reaction (KOH):

7.5.2.2 Required elements - CAG or CAGC unit - KOH solute - Distilled water - Beaker with a capacity of 0.5 or 1 L - Stirrer - Scale - Gloves, mask and safety glasses

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7.5.2.3 Experimental procedure 1.

Prepare a 5% KOH solution by pouring 50 grams of KOH in a beaker of 1 L (add distilled water till the mark). This amount of solution may be used to analyze at least 8 gaseous samples.

2.

Introduce the KOH solution in the U shaped tube (TU-U) (refer to the operating mode section).

3.

Fix the air and CO2 flow rate when both must be started at the same time according to the method explained in the operating mode section and record the flow values:

4.

Analyze the air current (there are three methods explained in the operating mode section: theoretical method, analytical method and CO2 meter).

5.

Record the mass concentration of CO2:

6.

Analyze 3 or 4 gas samples as it was explained in the previous steps for fixed flow rates of CO2 and air. Fill the working sheet attached below and answer the questions.

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7.5.2.4 Working sheet Student: ________

Year: __________

Table 2: % of CO2 absorbed by the solution at different flow rates Air %flowmeter CO2 %flowmeter Theoretical Experimental Meter (%mass) (%mass) (%mass)

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7.5.2.5 Working sheet Student: ________

Year: __________

Table 3: average % of CO2 absorbed by the solution at different flow rates Air %flowmeter CO2 %flowmeter Theoretical Experimental Meter (%mass) (%mass) (%mass)

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7.5.2.5 Working sheet Student: ________

Year: __________

Questions:

1. What does it happen when increasing the flow of CO2 for the same flow of air?

2. What does it happen when increasing the flow of air for the same flow of CO2?

3. For which flow rates is the lowest concentration of CO2 obtained? And the highest concentration of CO2? Are the results logic? Explain your answer.

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7.5.3 Practical exercise 3: Analysis of water samples 7.5.3.1 Objective To determine the concentration of CO2 in water by an acid-base titration. 7.5.3.2 Required material CAG or CAGC unit. - Chemical elements: o CO2 o 0.02M NaOH solution o Phenolphthalein - General instrumentation for the titration of liquids (phenolphthalein): beaker, scale, burette, dropping tube, etc. - Safety and prevention instrumentation: safety glasses, gloves, lab coat, etc.

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7.5.3.3 Experimental procedure 1.

Fix the flow of air and CO2 when both must be started at the same time according to the method explained in the operating mode section and record the flow values:

2.

Wait for 3 minutes until reaching the stationary state.

3.

Connect the water pump (AB-1).

4.

Fix and regulate the water flow according to the operating mode and record the flow value:

5.

Wait for 5 minutes until reaching the stationary state.

6.

Put the hose that leaves from the valve (V-9) facing the water storage tank (TAA).

7.

Close the regulation valve (VR-4) slightly.

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8.

Open the valve (V-9) and allow water to flow through the hose towards the tank (TAA).

9.

Watch and regulate the water level below the column (COL) with the valve (VR-4) so that the level is between MAX. and MIN. IMPORTANT: this step must be checked regularly when the valve (V-9) is opened or closed to take water samples.

10. Put a beaker at the outlet of the hose that leaves through the valve (V-9) and fill it with approximately 400 ml. At least three samples of 100 ml of water may be taken and analyzed from this beaker for each fixed flow. 11. Prepare a solution of NaOH 0.02M. For that end dilute 0.32 g of NaOH in 400 ml of distilled water. 12. Refill the graduated burette with a certain amount of the previously prepared solution. Record the initial volume of the burette: 13. Pour the water sample to be analyzed in an Erlenmeyer flask of 100 ml. 14. Add 10 drops of phenolphthalein indicator. If the sample turns pink, there is no CO2. If the sample remains colorless, add drop by drop the NaOH solution

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contained in the burette. 15. When the sample turns pink and remains pink, close the stopcock of the burette and record the new volume of the burette. 16. Calculate the volume of NaOH that has reacted: 17. Note down and adjust the reaction that takes place:

18. Calculate the concentration of CO2 in the water sample: Volume of the NaOH solution Concentration of the used solution of NaOH The molar concentration of CO2 in the sample will be:

As the concentration of CO2 is very small, it is assumed that the density of the sample is the same than the density of the solvent or water.

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19. Calculate the mole fraction of the sample:

20. All the analysis must be done three times. 21. Then, record the volume of NaOH solution employed for the titration of each water sample and calculate the average volume used:

22. Calculate and record the molarity of the sample:

23. Determine the moles of CO2 of the analyzed sample:

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24. Determine the moles of solvent of the analyzed sample: As the concentration of CO2 is very small:

25. Calculate the mole fraction of CO2 of the sample:

26. Repeat all the steps for different flows of water, air and CO2, as the ones shown in the table below, and answer the questions.

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Mol fracti (x2)

7.5.3.4 Working sheet Student: ________

Year: __________

Table 4: Calculation of the samples titrated. Air CO2 %flowmeter %flowmeter

50

30

30

30

30

50

50

30

30

30

30

50

Water (l/min)

ml of NaOH used in the Average titration

Molarity of the sample

moles CO in 100ml sample

1,3

2

2,6

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7.5.3.1 Working sheet Student: ________

Year: __________

Questions: 1. What happens when increasing the flow of CO2 for the same flow of air and water?

2. What happens when the air flow is increased for the same flow of CO2 and water?

3. What happens when the water flow is increased for the same flows of air and CO2?

4. For which flows is the lowest concentration of CO2 obtained? And the highest concentration? Are the results logical? Explain the answer.

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7.5.4 Practical exercise 4: Determination of the mass transfer coefficient for a packed column 7.5.4.1 Objective Determination of the mass transfer overall mean volumetric coefficients through the liquid phase and the influence of the flow of liquid on that coefficient. In our case, as the control is exerted by the liquid phase (water in this case) it will only be necessary to determine the mass transfer coefficient through the liquid phase (

).

7.5.4.2 Required material CAG or CAGC unit. - Chemical elements: o CO2 o 0.02M NaOH solution o Phenolphthalein - General instrumentation for the titration of liquids (phenolphthalein): beaker, scale, burette, dropping tube, etc. - Safety and prevention instrumentation: safety glasses, gloves, lab coat, etc.

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7.5.4.3 Experimental procedure 1.

Fix the flow of air and CO2 when both must be started at the same time according to the method explained in the operating mode section

2.

Wait for 5 minutes until reaching the stationary state.

3.

Record the flow rates:

4.

Determine the total flow of gas G (air and CO2) at the inlet of the column (COL) in the lower part:

5.

Analyze the air current according to the method explained in the operating mode section (theoretical method, analytical method and/or meter) and record the mole concentration of CO2 of the sample before starting the water circuit:

6.

Calculate and record the initial mole fraction:

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7.

Connect the water pump (AB-1).

8.

Fix and regulate the water flow according to the operating mode section.

9.

Wait 5 minutes until reaching the stationary state and control the water level below the tank. At that moment the absorption of CO2 in the water will start.

Record the value of the flow rate:

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Analyze the air current according to the method explained in the operating mode section (theoretical method, analytical method and/or meter) and record the mole concentration of CO2 of the sample after starting the water circuit:

Calculate and record the final mole fraction:

Put the hose that leaves from the valve (V-9) directed towards the water storage tank (TAA). Close the regulation valve (VR-4) slightly. Open the valve (V-9) and allow the flow of water through the hose towards the tank (TAA). Watch and regulate the water level below the column (COL) with the valve (VR-4) so that the level is between MAX. and MIN.

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IMPORTANT: this step must be checked regularly when the valve (V-9) is opened or closed to take water samples. Put a beaker at the outlet of the hose that leaves from the valve (V-9) and fill it with a little bit more than 300 ml. Three samples of 100 ml of water can be taken from the beaker for each established flow and analyze them (refer to acid-base titration in the operating mode section). Then record the volume of NaOH solution employed for titrating each water sample and calculate the average volume employed:

Calculate and record the molarity of the sample:

Determine the moles of CO2 of the analyzed sample:

Determine the moles of solvent of the analyzed sample:

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As the concentration of CO2 is very small:

Calculate the mole fraction of CO2 of the sample:

Obtain the flow of CO2 transferred to the water (coefficient N that will allow the student to calculate the transfer coefficient (KL)):

7.5.4.4 Calculation of the overall mass transfer coefficient 1. Calculate the partial pressures before and after water flows through the column: partial pressure at the inlet of the column given by:

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Being

the mole fraction at the inlet of the column.

partial pressure at the outlet of the column given by:

Being

the mole fraction at the outlet of the column.

2. Determine the inner volume of the empty column:

flow of CO2 absorbed by water specific area of packing per unit of volume of packing (m2/m3). For the size of Raschig rings employed: a = 440 m2/m3. 3. Calculate the mass transfer coefficient substituting data calculated before:

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7.5.4.6 Working sheet Student: ________

Year: __________

Table 6: Calculation of the total flow of liquid (water) that crosses the column (COL) and determination of the mole fractions at the outlet (x2 and y2) of the column (COL). Nº Exp.

Water (l/min)

1

2

1,3

3

4

5

6

2,6

L (kg/min)

ml of NaOH used in the titration

Average

Molarity moles CO2 of the in 100ml sample sample

N=flow of CO2 in (x2) measured water (mol/s)

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7.5.4.4 Working sheet Student: ________

Year: __________

Table 7: Calculation of the overall volumetric coefficient of mass transfer in liquid phase (KL) and recording of the measures indicated by the CO2 meter before and after the flow of water through the column (COL) for some preset flows of air and CO2. Nº Exp.

1

2

3

4

5

6

(y1) theoretical

Pi

Po

KL

Ybefore (%vol)

Yafter (%vol)

Ybefore Yafter (%mass) (%mass)=

Ybefore (%mol)

Yafter (%mol)=

(y2) measured

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7.5.4.4 Working sheet Student: ________

Year: __________

Questions: 1. What happens when increasing the flow of CO2 for the same flow of air and water?

2. What happens when increasing the flow of air for the same flow of CO2 and water?

3. What happens when increasing the flow of water for the same flows of air and CO2?

4. In which case is the mass transfer coefficient higher? And lower? Explain the answer.

5. In your opinion, how should an industrial packed column be to obtain a greater mass transfer?

6. Which type of gases could be employed to detect absorption? High solubility or low solubility gases?

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7.5.5 Practical exercise 5: Mass balance verification 7.5.5.1 Objective Check that the mass balance is verified for the packed column (COL). Mass balance:

Where, Flow of gas that crosses the column (air + CO2)

(g/min)

Flow of water that crosses the column

(g/min) (nondimensional)

Mole fraction of CO2 in the mixture (air + CO2) at the inlet of the column (COL) (lower part)

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(nondimensional) Mole fraction of CO2 in the mixture (air + CO2) at the outlet of the column (COL) (upper part) (nondimensional) Mole fraction of CO2 in the water at the inlet of the column (COL) (upper part). It is practically non-existent, water does not have CO2. (nondimensional) Mole fraction of CO2 in the water at the outlet of the column (COL) (lower part) 7.5.5.2 Required material - No material is required for this practical exercise. 7.5.5.3 Experimental procedure 1. Calculate the mole fraction at the outlet of the column (COL) (upper part) y2 from the mass balance with the results obtained in the practical exercise 4 (Calculation of the mass transfer coefficient) and compare them with the y2 of the meter: By the mass balance:

As the initial concentration of CO2 in the water is practically nonexistent, . Therefore:

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From the practical exercise for the determination of the overall mass transfer coefficient it could be obtained:

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7.5.5.4 Working sheet Student: ________

Year: __________

Questions: 1. Are the compared mole fractions similar?

2. Is the mass balance verified?

Table 9: Checking the mass balance. Nº EXP

G (g/min)

L (g/min)

(x1)

(x2)

(y2) measured

1 2 3 4 5 6

3. If there is any difference, what might it be due to? Explain the answer.

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7.6 ANNEXES 7.6.1 Assembly The main parts of the installation are: - Analysis panel. - Liquid circuit (water). - Gases circuit (air and CO2). - Measurement and analysis equipment. - Packed column. The packed column and part of the liquid circuit of the bottom of the column are disassembled for the delivery of the unit. The procedure to mount the column and the water circuit is described below:

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1. Put the transparent tubes that made up the water circuit, located at the bottom of the unit, at the outlet of the column as it is shown in the figure:

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For that purpose:

1

2

3

4

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2. Put the PVC plate with metallic mesh at the bottom of the column, supporting it horizontally on the glass narrowing. PVC plate with metallic mesh that supports the Raschig rings

COLUMN NARROWING

3. Introduce the packing in the column. The packing is Raschig rings of 10x10mm that must be supported by the PVC plate placed in the previous step. The packing level must not be higher than the black gasket at the top nor be in contact with the glass diffusion shower. The ideal height is 5 cm below the black gasket.

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5 cm

Packing

IMPORTANT: Introduce the Raschig rings smoothly to prevent them from breaking and glass shavings entering the unit. 4. Put the white gasket made of Teflon in the base that will support the column.

5. Locate the column in its place taking into account that the white gasket made of Teflon must be correctly located so that there are no leaks. Put the black flange at the bottom with the black float inside.

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6. Fix the column with the metallic clamp.

7. Screw the flange of the bottom of the column.

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8. Attach the head of the column, which contains the water diffusion shower, to the upper side of the column, taking into account that the white gasket must be placed between the head and the column to prevent leaks.

White Teflon gasket

9. Screw the black flange of the upper side of the column.

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10. Connect all the screws of the column as it is indicated in the picture:

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7.6.2 Filling the manometers 7.6.2.1 Manometer (M-1) 1. Fill a glass with the liquid to be introduced in the manometer. 2. Locate it at the bottom of the valve (V-7) and introduce the silicon tube in the vessel that contains the liquid.

3. Place the valve (VT-1) as shown below and push the plunger of the syringe (JE) to expel the air inside to the atmosphere.

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4. Put the valves (VT-1, VT-2, VT-3, VT-4, VT-5) as shown below:

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5. Open the valve (V-7) and pull the plunger of the syringe. The student will observe that liquid rises through the left hand branch of the manometer (M-1).

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6. Fill the left hand branch of the manometer (M-1) completely. 7. Close the valve (V-7) and rotate the valve (VT-1) in such a way that the manoneter (M-1) connect with the atmosphere, thus, the liquid inside will be evenly distributed between both branches:

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7.6.2.2 Manometer (M-2) 1. Fill a glass with the liquid to be introduced in the manometer. 2. Locate it at the bottom of the valve (V-8) and introduce the silicon tube in the vessel that contains the liquid.

3. Place the valve (VT-1) as shown below and push the plunger of the syringe (JE) to expel the air inside to the atmosphere.

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4. Put the valves (VT-1, VT-2, VT-3, VT-4, VT-5) as shown below:

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5. Open the valve (V-8) and pull the plunger of the syringe. The student will observe that liquid rises through the left hand branch of the manometer (M-2).

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6. Fill the left hand branch of the manometer (M-2) completely. 7. Close the valve (V-8) and rotate the valve (VT-1) in such a way that the manometer (M-1) connect with the atmosphere, thus, the liquid inside will be evenly distributed between both branches:

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7.6.3 Frequent problems  The KOH solution cannot be introduced in the U shaped tube (TU-U) up to

the graduated scale. Reason: The full stroke of the syringe is not enough to make all the required amount of solution rise in one time. Solution: Read how to introduce the solution in the U tube (TU-u) in the operating mode section.  Pushing the plunger of the syringe requires much effort (JE).

Reason: The gas sample and the liquid are in a closed circuit, there must be no leaks. Recommendation: Introduce the gas sample in several times. Do not try to reach the end of the syringe’s stroke (JE) with only one push to avoid leaks due to the pressure increase.  The analytical method with the syringe does not indicate a constant final

volume; every time the plunger is pushed it keeps on rising. Reason: There are leaks or air enters through a connection or valve. Solution: Seal all connections with grease, specially the area surrounding the plunger of the syringe (JE) and the tubes and hoses connections.  The column is not flooded.

Solution: First, fix the water flow rate, leave it run for at least one minute and, then, fix the air flow rate.