SIMULATION OF KAILASHTILLA II GAS PROCESSING PLANT

The simulation of Kailashtilla II gas processing plant (at Golapganj, Sylhet) was carried out using Hyprotech's standard simulator 'HYSIM'. During the plant simulation, some changes were made to the process flow diagram due to the limitation of the HYSIM simulator, which cannot handle the molecular sieve dehydration system. Laboratory tests are performed to obtain the reaction mechanism and kinetics of the process.

Some changes were made in the process flow sheet due to some limitation of the simulator, which was discussed.

Figure I: Flow chart of steps in simulation

LITERATURE REVIEW

HISTORICAL DEVELOPMENT

The first fifteen years of history in the development of flowsheet programs can be roughly divided into three five-year periods. Upadhye et al[5] developed a method for selecting the set of empty streams in a process simulation that leads to convergence of a direct substitution calculation in the least number of iterations. Lucia et aZ[14] investigated the asymptotic behavior of fixed point methods in the complex domain.

Through a skillful combination of science and art, a framework can be developed for an economic, quantitative and scientific approach to technical problems in the process industry.

SIMULATION MODELS

The mathematical model for any system under study can of course be programmed specifically for simulation on the digital computer and the resulting program can be used to duplicate any reasonable set of operating conditions, but simulation is so important that many general purpose problem-oriented solutions have been developed specifically for developed languages or programs in this field. Evans et al.[27] proposed the plex data structure for use in an advanced computer system to model chemical processes. The plex has been shown to enable greater modularity and flexibility over systems with dimensioned array structures.

Two methods are proposed for creating and running a plex: a problem-oriented language and problem-oriented calling programs.

PROCESS SIMULATION TECHNIQUES

Sequential Modular Approach
Simultaneous Modular Approach
Equation Oriented Approach

The main objective of the study was to demonstrate that the concurrent modular approach could be successfully applied. Several recent studies, including those by Perkins[16], Biegler and Hughes[17, 8] have shown the promise of the simultaneous modular approach for both flowsheeting and optimization problems. In the third part, the performance of the simultaneous-modular approach on four process optimization problems is studied, and numerical experiments with different computational strategies are also performed.

The simultaneous modular algorithm offers many advantages over the equation solving process when using existing sequential modular software.

Figure 2.3: Components of a simulation program.

THE FLOWSHEET SIMULATOR

All the user has to supply is the data, and the manager handles the program in the same way, regardless of the nature of the simulated process. Unfortunately, all device modules must be loaded into the computer's main memory, regardless of whether many of the routines are relevant to the process being simulated. Data storage space may only be allocated according to the size of the problem.

The input should consist of process topology, information on all input streams, design parameters of the units and convergence criteria.

THERMODYNAMIC AND PHYSICAL PROPERTIES

Structure of TP systems

Thus, during the calculation phase of the simulation, only the estimation parameters of the methods used for the specific set of chemical components present in the process need to be known to the TP package. Equipment modules can be developed without regard to the specific TP estimation procedures or components to be used, as the preprocessing phase of the simulation run will condition the TP package to use the correct options and components when TP generation is invoked. Where the system is widely used in the company, there is usually a support group of several people responsible for overseeing the accuracy and reliability of the estimation procedures used in the TP system.

Consequently, the user may need to select an option that is more valid in the dominant temperature range of the process.

APPLICATION OF FLOW SHEET SIMULATION

A New Way of Doing Process Development
Speed Commercialization
Retrofitting of a Liquid-Extraction Process
Ammonia Plant Operations
Design of a Feed-Forward Control System l21
Competitive Evaluation l2]
Reverse Engineering l2l
Raw-Material Bidding (2)
General Comments

The pilot plant was not used to prove the usefulness of the process carried out on the computer. Armed with the results of the flowsheet model, the development team was able to gain management approval to proceed with plant construction in record time. The leader of the development team was promoted to director of process development and is now the Vice President of the company.

To determine the optimal amount of solvent to use, engineers developed a model of the extraction process.

Figure 2.6.3: Flowsheet of liquid-extraction process

SUMMARY OF SOME SIMULATION PACKAGES

Summary of Some Simulation Packages[3]

PROCESSsM Simulation Program is a newly developed simulator based on many years of experience in providing simulation and design programs for the chemical and petroleum industries. Brannock et al.[24] described the basic features and illustrated several unique features using an industrial example. Hutchison et al.[19] described the design flow costs of using the equation-oriented simulation and optimization program QUASILIN.

They described in detail the problems on which simulation and optimization were tested and discussed the performance of the program.

DESCRIPTION OF THE 'HYSIM' SIMULATOR

OBJECTIVES OF THE THESIS WORK

DESCRIPTION OF 'HYSIM' SIMULATOR

HYSIM requires DOS 3.0 or later, at least 200 KB of normal memory, at least 3.5 MB of extended memory for version 386, at least 9 MB of disk space to store executable and data files to install and use HYSIM properly. .

PROCESS DESCRIPTION OF KAILASHTILLA II GAS PROCESSING PLANT (J- T MODE)

DESCRIPTION OF THE EXISTING PLANT (J-T MODE) [FIGURE ]

The upper product of the stabilizer (stream 16) is used as fuel gas and the lower product (stream 17) of the stabilizer is fed through the stabilizer product cooler (AC- 19.03). The exhaust gas stream (stream 20) from the dehydrator (PV-16.02 A/B) is then split into two streams, i.e. Then the exhaust streams are mixed and the mixed stream is fed through the cold separator (PV -16.03).

The top stream (stream 25) from the cold separator is passed through the J-T valve to reduce the pressure from 10340 kPa to 3450 kPa, and the bottom stream (stream 24) is passed through a valve to reduce the pressure, and the output streams are then mixed. The top stream (stream 29) from the expander separator is passed through the heat exchanger (HE-15.04) which is installed inside the deethanization column at the top. The top product (stream 31) of the de-ethanizer is mixed with stream 30 and then the mixed stream (stream 32) is passed through the gas-gas exchanger (HE-15.02).

The gas stream (stream 33) from the gas-gas exchanger is led through the Regeneration Gas Exchanger (HE-15.15).

TABLE 1: COMPOSITION OF THE FEED FROM THREE WELLS

DESCRIPTION OF THE SIMULATED PLANT (J-T MODE) [FIGURES A-I & A-II]

Then the product is pumped from the cooler (PM-17.Dl) and mixed with the bottom product (stream 46) of the de-ethanizer (PV-16.05) and stored in a storage tank and feeds the condensate to the LPG plant as required. Stream 26 is then passed through the gas-gas exchanger (HE-15.02), while stream 27 is passed through the deethanizer feed heater. The bottom stream is passed through the de-ethanizer feed heater (HE-15.03) and fed to the de-ethanizer (stream39).

The gas stream (stream 43) from the gas-gas exchanger is fed through the residue-gas compressor (CM-11.01) and then the residue-gas cooler (AC- . 19.04).

METHODOLOGY OF SIMULATION

In contrast, HYSIM tracks available information from module to module as it is specified or calculated. Most unit operations can calculate backwards (i.e., determine feed stream properties from known product stream values). Unit operations link streams together in a flow chart, in a similar way to the way actual pieces of equipment link streams in a plant.

HYSIM unit operations are information processing modules, which determine how the flows associated with them are related in properties. For a simple valve, the module would know that the flow, composition and intensive enthalpy of the two streams connected to it must be the same. So if any of these properties were known for one of the connected flows, the valve could assign the values to the other flow.

The valve itself knows nothing about the temperatures and pressures of the connected streams, but the property package module, which monitors all changes in stream information, would notice that new information is available for the stream. For example, if the stream pressure was previously known and the valve now provided the enthalpy and composition, the properties package would go ahead and determine the stream temperature and other properties. If too much information is given and it is not consistent, an error message is displayed.

For example, if the temperature and pressure had been known when the valve supplied the enthalpy and composition, an error would result unless the temperature turned out to be exactly correct. It is noted that since the unit operations are actually information processors, it is possible to have more than one unit operation in parallel.

RESULTS AND DISCUSSIONS

RESULTS AND DISCUSSION

Two process flow diagrams are shown (Figures A-I and A-II) and the installation is simulated in these two alternative ways. The sales gas compositions are exactly the same (stream 45, appendix I and II, pages 93, HI) using the two alternative methods. In the first process (dehydration of gas by cooling), a small fraction of water remains in the gas after cooling and this water is separated again in a separator (sepa 3) [Figure A-I].

So, finally, the second process (dehydration of gas by component splitter) is considered to check the design data and to study the performance of the plant using the operating data. Due to the changes in the process flow diagram, some small differences appeared in the result based on the design data shown in Table 4. But finally, the sales gas composition and NGL composition are almost the same as the design data, which are shown in Tables 2 and 3 respectively.

In the process flow diagram, the heat exchanger (HE-15.04) is installed in the de-ethanizer column. Some differences occurred at different stages of the outcome, which are shown in Table 5 and worksheets in Appendix III (page 113). In addition, the HYSIM simulator does not take into account the length of the pipe (pressure drop due to friction and other losses) or pipe heat loss during the simulation.

For this reason, studying the operating data using the HYSIM simulator would lead to slightly different results and these would indicate the operability and performance of the installation, compared to design values.