Pinch Technology By Shubham

PRESENTED BY Shubham Aggarwal (4th yr.) Chetan Aggarwal (3rd yr.) Seth Jai Prakash Mukand Lal Institute Of Engineering & Technology Radaur,Kurukshetra University Kurukshetra Haryana

Contents • Introduction • Techniques available for process integration • Pinch technology • Features and Benefits of Pinch • Where pinch technology is used? • Concept of pinch technology • Phases of pinch technology • A Retrofit Project

PROBLEMS OF PROCESS INDUSTRY RELATED TO ENERGY •

Borrowed, often obsolete technology

•

Energy consumption per unit production much higher than in western industries

•

No concept of process integration

ENERGY MANAGEMENT THROUGH PROCESS INTEGRATION - A REALITY • Problems of Indian industries can be solved by using techniques that minimize energy consumption with minimum investment. • Process integration is one such technique.

PROCESS INTEGRATION The Process Integration is defined as “Systematic and general methods for designing integrated production systems, ranging from individual processes to total sites, with special emphasis on the efficient use of energy and reducing environmental effects”. Process Integration is a part of Process Intensification (PI). Ramshaw, 1995, defined PI as: “A strategy for making dramatic reductions in the size of a chemical plant so as to reach a given production objective”.

Techniques available for process Integration 

Pinch Technology Approach



MILP/MINLP Approach



State-Space Approach



Genetic Algorithm Approach



Process Graph Theory Approach



Supertargeting Approach

Methods in Process Integration The three major features of Process Integration methods are: • The use of heuristics (insight) • The use of thermodynamics • The use of optimization techniques. Pinch Analysis is a method with a particular focus on Thermodynamics. Hierarchical Analysis and Knowledge Based Systems are rule-based approaches with the ability to handle qualitative (or fuzzy) knowledge. Finally, Optimization techniques can be divided into deterministic (Mathematical Programming) and non-deterministic methods (stochastic search methods such as Simulated Annealing

QUALITATIVE

One possible classification of Process Integration methods is to use the two-dimensional (automatic vs. interactive and quantitative vs. qualitative) representation in figure 1.

Knowledge Based Systems

Heuristic Rules

Hierarchic al Analysis

AUTOMATIC Optimization Methods

INTERACTIVE

Thermodynamic Methods

QUANTITATIVE

Fig. 1 One possible Classification of Process Integration Methods

PINCH TECHNOLOGY Pinch Technology was introduced by Linnhoff in 1978 to solve heat exchange problems as an energy saving tool. Pinch Technology forms the essence of optimization of processes by energy and resource analysis (OPERA). Pinch technology reveals all the possible savings and their corresponding financial benefits. • • •

It defines the maximum possible savings. It looks at the overall site. It does not bench-mark but takes into account all specific mill factors, age, location, process equipment, operating preferences, product, etc.

•

It reveals the maximum cogeneration potential

Features and Benefits of Pinch… •

Targets for minimum heating & cooling.

•

Quantifies scope for heat recovery.

•

Analysis Includes the process unit or the whole site, as appropriate:

•

Design tools define appropriate project.

•

Shows what to do with low-grade waste heat.

•

Combined Heat and Power (CHP).

•

Practical application brings real benefits.

WHERE PINCH TECHNOLOGY IS USED? 

     

Heat integration Distillation column targeting Cogeneration & total site targeting Batch process targeting Emission targeting Mass exchange network ( Water & waste water management & recovery of valuable materials) Hydrogen management in refineries

CONCEPT OF PINCH TECHNOLOGY

ONION DIAGRAM

Fig. 2. The process design hierarchy can be represented by “onion diagram” as shown below. 1 2 3

4

Reactor Separator Heat exchange network Utilities

Site-Wide Utilities

Fig. 2 Onion Diagram

The heat and material balance is at this boundary

Main points from onion diagram

Design of a process starts with the reactors. Separator can be designed for known feeds, products, recycle concentrations and flow rates. For heat and material balance, heat exchange network (HEN) can be designed. For remaining heating and cooling duties, the utility system is designed.

PROBLEM ADDRESSED Generally two types of problem are addressed: • Creating New Designs This is related to the design of HEN for a new plant, which is in design stage. • Retrofit – Revamping Existing Designs This is related to the retrofitting of an already existing HEN in a plant to improve its exchange efficiency.

PHASES OF PINCH TECHNOLOGY

There are four phases of pinch analysis in the design of heat recovery systems for both new and existing processes: DATA EXTRACTION It relates to the extraction of information required for pinch technology from a given process heat and material balance.

PERFORMANCE TARGETS Targeting provides a fundamental insight into heat recovery options in a process. It does this by giving a system-wide view of the heating and cooling requirements at different temperature levels.

NETWORK DESIGNING In design the user will typically work with an incomplete network and try to follow the pinch design rules.

NETWORK OPTIMIZATION Heat exchange network for maximum energy recovery established by pinch design method, should only be regarded as initial designs and some final optimization is required.

Graphical Representation Composite curve 200

Region of heat recovery by process to process exchange

QHmin

T (C)

150 ∆Tmin

100 50

Above pinch

Below pinch

QCmin

HCC CCC

0 0

1000

2000

3000

4000

Heat Content Q (kW) Fig. 6. The HCC and CCC show the heat availability and heat requirement for the overall process

5000

Analytical Procedure Problem Table Algorithm (PTA) For the calculation of energy targets, only the inlet temperatures, outlet temperature and heat capacity flow rates are required. The steps involved in PTA are: •

Determination of temperature intervals

•

Calculation of net MCP in each interval MCp,int = Σ MCp,c – Σ MCp.h

for each interval

•

Calculation of net enthalpy in each interval

•

Calculation of cascaded heat

•

Revision of cascaded heat

•

Determination of energy targets

Implementation of Problem Table Algorithm Interva l i.

Col. A Tint

Col. B MCp,int

Col. C Qint

Col. D Qcas

Col. E Rcas

0 1 2 3 4 5 6

165 122 115 55 50 35 30

0 10 25 -15 25 10 20

0 430 175 -900 125 150 100

0 -430 -605 295 170 20 -80

605 175 0 900 775 625 525

stream MCp

H1 10

H2 40

C3 20

C4 15

Concept of Pinch The composite curve gives the information as: Minimum hot utility (QHmin) = 605 kW Minimum cold utility (QCmin) = 525 kW Hot pinch temperature = 125 ˚C Cold pinch temperature = 105 ˚C

∆Tmin is known as the “pinch” and once the pinch is recognized it is possible to consider the process as two separate systems: one above the pinch and one below the pinch. The system above the pinch requires a heat input and is therefore a net heat sink. Below the pinch, the system rejects heat and so is a net heat source.

Concept Of Multiple Utility The energy requirement for a process is supplied via several utility levels e.g. steam levels, refrigeration levels, hot oil, furnace flue gas etc. The general objective is to maximize the use of the cheaper utility levels and minimize the use of the expensive utility levels. The composite curve provide overall energy targets but do not clearly indicate how much energy needs to be supplied by different utility levels. For this purpose, the grand composite curve is used.

Grand Composite Curve 180

HU1

160 140

HU2

High temperature process sink profile

120 T (*C )

100

Low temperature process source profile

CU2

Pinch

Process to process heat exchange

80 60 40 20

CU1

0 0

100

200

300

400

500

600

700

800

Heat flow Q (kW)

Fig. 7. GCC shows the multiple utilities

900

1000

The balanced composite curve is generated to estimate the targeted area.

T (C)

BALANCED COMPOSITE CURVES 200 180 160 140 120 100 80 60 40 20 0

Th,i. BHCC Th,i.-1

Interval i.

Tc,i. BCCC

Tc,i.-1

0

1000

2000 3000 Heat Content Q (kW) Fig.8. The balenced composite curves

4000

5000

Fig. 4: Potential energy savings in some major industrial sectors

Fig. 5: Potential water consumption savings in some major industrial sectors

A RETROFIT PROJECT Even in a simple process made up of two unit operations (Fig. 6 & 7), a reactor and separator, with a recycle stream, pinch technology has something to offer. In this case, a pinched design (right) reduces steam consumption by 38%, eliminating the need for external water cooling, cutting the number of heat exchangers needed from six to four, and reducing heat transfer surface area requirements from 629 to 533 m2.

Unpinched

Pinched process

Reactors

Reactors

Steam

Steam Recycle

Recycle Steam

Separator

Separator

Product Feed Cooling mater

Figure.6

Product

Feed

Figure.7

RETROFIT PROJECT The pinch technology principle is applied on various projects. One such project, Fig. 8, consists of a complex refining system. The process is already highly integrated, with various streams being heat-exchanged to reduce overall energy requirements. Application of pinch technology in this project results a minimum energy target of about 31 MW for the hot utility, which is steam. The original process consumed nearly 39 MW of steam. Thus, the “scope” for improvement is 8 MW or 20% of original demand. A brief analysis of the existing flow sheet uncovered the specific reasons for current utility requirements being greater than the target: 1. One instance of utility heating below the pinch. 2. One instance of utility cooling above the pinch. These violations totaled 8MW. If eliminated, they would bring the utility requirements to target. The problem was, it would take six new exchangers and a substantial new investment to accomplish this.

Recycle

17,000 lb/hr Steam

Feed and recycle Recycle 20 psi

Steam

1

2

Reactor Flash Preheater

Stripper

Fig. 8 Process prior to retrofit.

70 psi 3

4

5

At this stage, one should always look for “process modifications” that included the following: 1. 2.

Decrease the pressure of column No. 2 by 5 psi (34 kPa). Decrease the pressure of column No. 5 by 10 psi (69 kPa).

The effect of these modifications resulted the energy target for the process so modified was 27 MW representing another 15 % potential savings. The problem was, it would still take six new exchangers and a substantial new investment to accomplish this. At this stage, one should look for “second order” process modification aimed at simplifying the necessary hardware changes. Modify the process slightly so that its enthalpy changes fit as many of the existing exchangers as possible? These major adjustments led to the sacrifice of 1.3 MW but helped to save four exchangers reducing the number of new exchangers from six to two. The flow sheet for the process finally recommended is shown in Fig. 9. Process modifications and two new exchangers combined give 28 % energy savings at six months payback.

Feed and recycles

11,000 lb/hr Steam

New exchangers 15 psi

Steam

1

2

Reactor Flash Stripper Preheater Recycle

Fig. 9 The process after retrofit.

60 psi 3

4

5

CONCLUSIONS With all of the tools that pinch analysis provides, one of the most important challenges before is to properly integrate pinch tools into the conceptual process design phase. Decisions made in the phase of planning affect the entire life cycle of a process facility. Using pinch technology tools & understanding the process doesn’t ensure the desired results. These tools must be applied at the right point in the process design phase. Just as it be incorrect to conduct a pinch analysis after completion of the process design phase, wherein critical process parameters have been fixed, it is just as incorrect to conduct a pinch analysis without a direct interaction with the process specialists & downstream engineering disciplines. It is Pinch Technology’s role to identify “what might be”. However, input from other engineering disciplines ultimately determines “what can be”.

REFERENCES 1.

Plant Design And Economics For Chemical Engineers Max S Peter,Ronal E West 5th Edition,McGraw Hill

4.

Richardson & Colson Vol.6

6.

Genaral Process Improvement Through Pinch Technology B.linnoff , G.T pollen