SIMULATION OF NITROGEN LIQUEFICATION CYCLES A PROJECT REPORT SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF Master of Technology in Thermal Engineering by SHAILESH PRASAD Roll-207ME313 Department of Mechanical Engineering National Institute of Technology Rourkela 2008-2009 SIMULATION OF NITROGEN LIQUEFICATION CYCLES A PROJECT REPORT SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF Master of Technology in Thermal Engineering by SHAILESH PRASAD Roll-207ME313 Under The Guidance of Prof. Sunil Kumar Sarangi Department of Mechanical Engineering National Institute of Technology Rourkela 2008-2009 Dedicated to my mom & dad National Institute of Technology, Rourkela CERTIFICATE This is to certify that the thesis entitled, “simulation of nitrogen liquefication cycles” submitted by Shailesh Prasad in partial fulfillment of the requirements for the award of MASTER OF TECHNOLOGY Degree in Mechanical Engineering with specialization in “Thermal Engineering” at the National Institute of Technology, Rourkela (Deemed University) is an authentic work carried out by him/her under my/our supervision and guidance. To the best of my knowledge, the matter embodied in the thesis has not been submitted to any other University/ Institute for the award of any degree or diploma. Date: Prof. S.K.Sarangi Department of Mechanical Engg. National Institute of Technology Rourkela - 769008 I ACKNOWLEDGEMENT First I would like to express my deep appreciation and gratitude to Prof. S.K. Sarangi for his constant support and exceptionally helpful guidance throughout this study. Working under his supervision greatly contributed to improving the quality of the thesis and to developing my general engineering and management skills. Further I greatly appreciate the help from Prof. R.K.Sahoo whose technical expertise in the heat transfer area constituted a valuable asset. I also want to take this opportunity to express my appreciation toward Prof. A.K.Sathpathy. for his valuable suggestions and encouragement throughout the project work. I thank all my friends in Mechanical Engineering for making my stay at N.I.T.Rourkela a pleasant and memorable experience. SHAILESH PRASAD Roll No. 207ME313 Department of Mechanical Engg National Institute of technology II CONTENTS CERTIFICATE I ACKNOWLEDGEMENT II CONTENTS III ABSTRACT VI LIST OF FIGURES VII LIST OF TABLES IX NOMENCLATURE X 1. INTRODUCTION 1 1.1 Gas liquefaction systems 2 1.2 System performance parameters 3 1.3 Refrigeration efficiency 3 1.4 The thermodynamically ideal system 4 1.5 Production of low temperatures 6 2. LITERATURE SURVEY 8 2.1 Simple Linde-Hampson systems 9 2.1.1 Working principle 10 2.1.2 Performance of system 11 2.2 Claude system 11 2.1.1 Performance of system 13 III 2.3 The Kapitza system 15 2.4 The Heylandt system 15 3. ASPENONE 18 3.1 Introduction 18 3.2 Aspen-ONE engineering 19 3.3 Introduction to Aspen Hysys 19 3.4 Equation of state 20 3.4.1 Peng-Robinson 21 3.4.2 BWRS 23 3.5 Simulation Environment 23 3.6 The components or the blocks or the equipments 24 3.6.1 HYSYS object 24 A. Mixer. 24 B. Compressor 25 C. Cooler/Chiller 25 D. Heat Exchanger / LNG 25 E. Separator 25 IV 3.6.2 Logical Units 27 A. Set 27 B. Spreadsheet 27 C. Recycle 28 4. RESULT AND DISCUSSION 4.1 Simulation of Linde cycle 4.1.1 30 Figure of merit 33 4.2 Simulation of Claude cycle 34 4.3 Simulation of Kapitza cycle 42 4.4 Simulation of Claude cycle for Haylent 46 4.5 Simulation of Haylent system 47 5. SIMULATION OF LN2 PLANT 50 5.1 LN2 plant at NIT-Rourkela 51 6. CONCLUSION 55 REFERENCE 57 V Abstract System simulation is the calculation of operating variables such as pressure, temperature and flow rates of energy and fluids in a thermal system operating in a steady state. The equations for performance characteristics of the components and thermodynamic properties along with energy and mass balance form a set of simultaneous equations relating the operating variables. The mathematical description of system simulation is that of solving these set of simultaneous equations which may be non-linear in nature. Simulation is not needed in design conditions because in the design process the Engineer probably chooses reasonable values of the operating variables and selects the components that correspond to operating variables. Cryogenics is the branch of engineering that is applied to very low temperature refrigeration applications such as in liquefaction of gases and in the study of physical phenomenon at temperature of absolute zero. The various cryogenic cycles as Linde cycle, Claude’s cycle , Stirling cycle etc govern the liquefaction of various industrial gases as Nitrogen, Helium etc. We have the operating conditions and operating variables which can be solved numerically which is tedious. The following work aims to simulate the nitrogen liquefication cycles with the help of the simulation tool ASPEN HYSYS where all calculations are done at steady state and the results hence obtained. VI LIST OF FIGURES Figure Title page 1.1 The thermodynamically ideal liquefication system 5 (a) Thermodynamic cycle T-S plane, (b) Apparatus setup 2.1 Linde-Hampson liquefication system 9 2.2 Linde-Hampson liquefication cycle (T-S plot) 10 2.3. The Claude system 12 2.4 Claude cycle (T-S) plot 12 2.5. The Kapitza system 15 2.6. The Haylent system 16 3.1 Industries and Business Areas of aspenONE 18 3.2 aspenONE engineering classification 19 3.3 Simulation environment 23 4.1 PFD of Linde cycle 30 4.2 Yield vs pressure plot for linde system 42 4.3 variation of yield with minimum approach of heat exchanger 32 4.4 Claude PFD 34 4.5 Work required liquefying a unit mass of nitrogen in the Claude system 36 (a) Full plot (b) Magnify plot VII Figure Title page 4.6 Temperature profile in heat exchanger at optimum value 37 4.7 Claude PFD with effectiveness in first HX 38 4.8 Optimum work required liquefying a unit mass of nitrogen in the 40 Claude system 4.9 Kapitza PFD 43 4.10 Optimum work required liquefying a unit mass of nitrogen in the 44 Kapitza system 4.11 Comparison of work required to liquefy unit mass of nitrogen 45 4.12 Optimum work required liquefying a unit mass of nitrogen in the 47 claude-Haylant System 4.13 Haylent PFD 48 4.14 Optimum work required liquefying a unit mass of nitrogen in the 49 Haylent system 5.1 LN2 plant PFD 51 VII List of table Table Title Page 4.1 Variation of yield with pressure 31 4.2 Variation of yield with minimum approach of heat exchanger 32 4.3 Net works required to liquefy nitrogen at different value of x without 35 effectiveness 4.4 Net works required to liquefy nitrogen at different value of x with 39 effectiveness 4.5 Temperature across heat exchanger at different value of x 41 4.6 Net works required to liquefy nitrogen at different value of x for 43 kapitza system 4.7 Net works required to liquefy nitrogen at different value of x for 46 Claude system 4.8 Net works required to liquefy nitrogen at different value of x for 48 Haylent system 5.1 Optimum work required at various combination of efficiency of turbine, minimum approach and effectiveness of heat exchange of LN2 plant IX 54 Nomenclature = mass flow rate = heat transfer = work transfer f= liquid mass flow rate T = temperature y = yield ε = effectiveness C = heat capacity rate p = pressure v = volume R= universal gas constant Geek Symbols ρ = density γ = adiabatic index Subscripts C= cold fluid h = hot fluid Abbreviations HX = heat exchanger X CHAPTER: 1 INTRODUCTION 1 1.1 Gas liquefaction systems Liquefaction of gases includes a number of phases used to convert a gas into a liquid state. The processes are used for scientific, industrial and commercial purposes. Many gases can be put into a liquid state at normal atmospheric pressure by simple cooling; a few, such as carbon dioxide, require pressurization as well. Liquefaction is used for analyzing the fundamental properties of gas molecules (intermolecular forces), for storage of gases, for example: LPG, and in refrigeration and air conditioning. There the gas is liquefied in the condenser, where the heat of vaporization is released, and evaporated in the evaporator, where the heat of vaporization is absorbed. Ammonia was the first such refrigerant, but it has been replaced by compounds derived from petroleum and halogens. Liquid oxygen is provided to hospitals for conversion to gas for patients suffering from breathing problems, and liquid nitrogen is used by dermatologists and by inseminators to freeze semen. Liquefied chlorine is transported for eventual solution in water, after which it is used for water purification, sanitation of industrial waste, sewage and swimming pools, bleaching of pulp and textiles and manufacture of carbon tetrachloride, glycol and numerous other organic compounds. Liquefaction of helium (4He) with the Hampson-Linde cycle led to a Nobel Prize for Heike Kamerlingh Onnes in 1913. At ambient pressure the boiling point of liquefied helium is 4.22 K (-268.93°C). Below 2.17 K liquid 4He has many amazing properties, such as climbing the walls of the vessel, exhibiting zero viscosity, and offering no lift to a wing past which it flows. 2 The liquefaction of gases is a complicated process that uses various compressions and expansions to achieve high pressures and very low temperatures; using for example turbo expanders. The liquefaction of air is used to obtain nitrogen, oxygen and argon by separating the air components by distillation. This chapter discusses several of the systems used to liquefy the cryogenic fluids. We shall be concerned with the performance of the various systems, where performance is specified by the system performance parameters or payoff functions. 1.2 System performance parameters There are three payoff functions we might use to indicate the performance of the liquefaction systems: 1. Work required per unit mass of gas compressed , 2. Work required per unit mass of gas liquefied , 3. Fraction of the total flow of gas that is liquefied. 1.3 Refrigeration Efficiency It is desirable to have a method of comparing real refrigerators with the ideal refrigerator. It is of intrest to know the maximum efficiency that can be achieved by such an engine operating between two reservoir at different temperatures. The French engineer Carnot describe an engine operating in particularly simple cycle knows as Carnot cycle. 3 The performance of real refrigerator is measured by the coefficient of performance (COP), which is define as the ration of refrigeration effect to the work input, the inverse of the efficiency term. Thus, = COP = (1.1) The figure of merit (FOM) is still another means of comparing the performance of practical refrigeration and is define as FOM = = Where COP is the coefficient of performance of the actual refrigerator system and COPideal and COPcarnot is the coefficient of performance of the thermodynamically ideal system and Carnot refrigerator, respectively. The figure of merit for a liquefier is generally written as FOM = 1.4 The thermodynamically ideal system In order to have a means of comparison of liquefaction systems through the figure of merit, we shall first analyze the thermodynamically ideal liquefaction system. This system is ideal in the thermodynamic sense, but it is not ideal as far as practical system is concerned. The perfect cycle in thermodynamics is the Carnot cycle. Liquefaction is essentially an open system process, therefore for an ideal liquefaction we shall choose the first two processes in the Carnot cycle; a reversible isothermal compression followed by a reversible isentropic expansion. The gas to be liquefied is compressed reversibly and isothermally from ambient conditions to some high pressure. This high pressure is selected so that gas will become saturated liquid upon 4 reversible isentropic expansion through the expander. The final condition is taken as the same pressure as the initial pressure. The pressure attained at the end of isothermal compression is extremely high in the order of 70Gpa and it is highly impracticable to attain this pressure in a liquefaction system, which is the reason it is not an ideal process for a practicable system. Temp Entropy (a) (b) Figure: 1.1 The thermodynamically ideal liquefication system (a) Thermodynamic cycle T-S plane, (b) Apparatus setup The First law of thermodynamic for steady flow may be written as: net - net = - (1.1) Applying the First law to the system shown in figure: R - 1 = (hf-h1) = - (h1-hf) (1.2) 5 The heat transfer process is reversible and isothermal in the Carnot cycle. Thus, from the second law of Thermodynamics R= T1 (s2-s1) = - T1 (s1-sf) (1.3) Because of process form point 2 to f is isentropic, s1=sf where s is the entropy of the fluid. Substituting R from equation (1.3) into equation (1.2) we may determine the work requirement for the ideal system. = T1 (s1-sf) – (h1-hf) (1.4) 1.5 Production of low temperatures Joule Thompson effect Most of the practical liquefaction systems utilize an expansion valve or a Joule Thomson valve to produce low temperatures. If we apply the first law for steady flow to the expansion valve, for zero heat transfer and zero work transfer and for negligible kinetic and potential changes, we fine h1= h2 .Although the flow within the valve is irreversible and is not an isenthalpic process, the inlet and the outlet do lie on the same enthalpy curve. We note that there is a region in which an expansion through the valve produces an increase in temperature, while in another region the expansion results in a decrease in temperature. Obviously we should operate the expansion valve in a liquefaction system in the region where there is a net decrease in temperature results. The curve that separates two regions is called the inversion curve. The effect of change in temperature for an isenthalpic change in pressure is represented by the Joule-Thompson coefficient. 6 Adiabatic expansion The second method of producing low temperatures is the adiabatic expansion of the gas through a work producing device, such as an expansion engine. In the ideal case, the expansion would be reversible and adiabatic and therefore isentropic. In this case we can define the isentropic coefficient which expresses the temperature change due to a pressure change at constant entropy. Existing Gas liquefaction systems Of the various gas liquefaction techniques developed by various cryogenic experts, some of them are listed below:1: Simple Linde Hampson system 2: Precooled Linde Hampson system 3: Linde dual pressure system 4: Cascade system 5: The Claude system 6: The Kaptiza system 7: The Collins liquefaction system 7 CHAPTER: 2 LITERATURE SURVEY 8 2.1 Simple Linde-Hampson system The Linde-Hampson system was the second used to liquefy gases (the cascade system was the first ), although it is the simplest of all the liquefication system is show in figure 2.1 and cycle is show in T-S plane in figure2.2 Fig: 2.1 Linde-Hampson liquefication system A basic differentiation between the various refrigeration cycles lies in the expansion device. This may be either an expansion engine like expansion turbine or reciprocating expansion engine or a throttling valve. The expansion engine approaches an isentropic process and the valve an isenthalpic process. Isentropic expansion implies an adiabatic reversible process while isenthalpic expansions are irreversible. In the Linde system, the basic principle of 9 isenthalpic expansion is also incorporated where as in Claude‟s cycle involves both isentropic and isenthalpic expansion procedure. Fig: 2.2 Linde-Hampson liquefication cycle (T-S plot) 2.1.1 Working principle The air enters the compressor through air pump which forced into compressor and compressed thereby being heated. The heat is removed in the cooling apparatus may be air cooled or water cooled and the compressed air finally reach to ambient temperature. Then it pass through counter flow heat exchanger where it temperature decrease below inversion temperature of working fluid. The air therefore reaches the J-T valve so that it expand through valve , so that 10 it constantly falling in temperature, reaches at lower and lower temperature and eventually the critical temperature of the liquid air is reached and liquid air begins to collect in chamber . 2.1.2 Performance of system In order to analyze the performance of the system, let us assume ideal condition: no irreversible pressure drops (except for the expansion valve), no heat inleak from ambient conditions, and 100 percent effective heat exchanger. Applying the first law for steady flow to the combine heat exchanger, expansion valve, and liquid receiver, we obtain 0=( - f) h1 + fhf - h2 (4.1) Solving for the fraction of the gas flow that is liquefied =y= (4.2) The fraction of gas liquefied (the liquid yield) thus depend upon: 1) The pressure and temperature at ambient condition (point 1), which fix h1 and hf 2) The pressure after the isothermal compression, which determines h2 because the temperature at state points 2 is specified by the temperature at point 1 2.2 Claude system The expansion through an expansion valve is an irreversible process, thermodynamically speaking. Thus if we wish to approach closer to the ideal performance, we must a better process to produce low temperatures. In the Claude system, energy is removed from the gas stream by 11 allowing it to do some work in an expansion engine or expander. The Claude cycle is shown in figure2.3 Fig: 2.3. The Claude system Fig: 2.4 Claude cycle (T-S) plane 12 An expansion valve is still necessary in the Claude system because much liquid cannot be tolerated in the expander in the actual system. The liquid has much compressibility than the gas, therefore, if liquid were formed in the cylinder of an expansion engine (positive displacement type), high momentary stress would result. Some rotary turbine expanders (axial-flow type) have developed that can tolerate as much as 15% liquid by weight without damage to the turbine blade In some Claude systems, the energy output of the expander is used to help compress the gas to be liquefied. In most small scale system, the energy is dissipated in the brake or in an external air blower .whether the energy is wasted or not does not affect the liquid yield; however, it does increase the compression work requirement when the expander work is not used 2.2.1 Performance of system Applying the first law for steady flow to the heat exchangers, the expansion valve, and liquid receiver as a unit, for no external heat transfer 0=( - f) h1 + fhf + ehe - h2 - eh3 (5.1) If we define the fraction of the total flow passes through the expander as x, or x= (5.2) Then liquid yield can be obtain form equation (5.1) as =y= +x (5.3) Again we see that the second term represent the improvement in performance over the simple Linde-Hampson system. 13 The work requirement per unit mass compressed is exactly the same as that of the LindeHampson system if the expander work is not utilized to help in the compression. If the expander work is used to aid in the compression, then the net work requirement is given by = (5.4) Applying the first law for steady flow to the expander, we obtain the work expression e= (h3- he) (5.5) If the expander work is utilize to aid I compression, the net work is given by = [T1 (s1-s2) – (h1-h2)] – x (h3-he) (5.6) In claude system of 3 heat exchanger setup we can find that there is phase change in second and thirds heat exchanger so that we can apply effectiveness term directly , only first heat exchanger have freedom to use effectiveness and minimum temperature approach to solve it, so effectiveness of heat exchanger is define as: “The ratio of the actual heat transfer to the heat transfer attainable in an infinitely long counter flow exchanger” ε= = (5.7) 14 2.3 The Kapitza system Kapitza (1939) modified the basic Claude system by eliminating the third heat exchanger or low temperature heat exchanger. Several notable practical modifications were also introduced in this system a rotary expansion engine was instead of reciprocating expander. The first or high temperature heat exchanger in the kapitza system was actually a set of valved regenerators, which combined the cooling process with the purification process. The incoming warm gas was cooled in one unit and impurities were deposited there, while the outgoing stream warmed up in the other unit and flushed out the frozen impurities deposited in it. Fig: 2.5. The Kapitza system 2.4 The Haylent system Helandt (Davies 1949) noted that for high pressure of approximately 20Mpa (200 atm) and an expansion engine flow ratio of approximately 0.60, the optimum value of temperature before expansion through the expander was nearly ambient temperature. Thus one could eliminate the first heat exchanger in Claude system by compressing the gas to 200 Mpa. Such a modified 15 Claude system is called the Heylandt system after its originator, and is use extensively in highpressure liquefication plant for air Fig: 2.6. The Haylent system 16 Chapter: 3 ASPEN-One 17 3. AspenONE 3.1 Introduction aspenONE is AspenTech‟s comprehensive set of software solutions and professional services designed to help process companies achieve their operational excellence objectives. It leverages the value of simulation models to help process companies increase operational efficiency and profitability across their global enterprise. Aspen-one cover four major field as shown in figure:2.1 , Chemical , Energy , Polymer , Pharmaceuticals. Pharmaceuticals Polymers aspenONE Chemicals Energy Fig: 3.1 Industries and Business Areas of aspenONE 18 3.2 Aspen-ONE engineering Aspen Plus Aspen APLE Aspen Dynamics Aspen FIHR Aspen PIPE aspenONE Engineering Aspen MUSE Aspen ACOL Aspen HYSYS Aspen HTFS Aspen TASC Aspen FRAN Fig: 3.2 aspenONE engineering classification 3.3 Introduction to Aspen Hysys The simulations of the Nitrogen liquefaction cycle have been carried out using Aspen Hysys, which is chemical process simulation modeling software. The flow sheet (PFD) includes a library of standard unit operation blocks and logical units (e.g. cooler, mixer, Heat-exchangers, separator, splitters, compressor, Recycle, spreadsheet, set, adjust), which represent processes taking place in an actual liquefaction plant. HYSYS is a combination of tools that are used for estimating the physical properties and liquid-vapour phase 19 Equilibrium of various inbuilt components. These components are the substances that are used within the plant for the feeds, within the reaction and separation sections. The program is such that it will converge energy and material balances and has standard unit operations typical of any processing plant. HYSYS updates the calculations as the user enters information and does as much as it can at that time. The successful completion of an operation is seen by the changes in colour on screen. HYSYS is not just a steady state program. A case can be transferred into a dynamic simulation where process controllers can be added, and hence, realistically evaluate a plant wide control philosophy For the Liquefaction process to be modelled in HYSYS, there must be a foundation on which the components must be modeled. In this process, there are one components involved in the chemistry that is nitrogen. Nitrogen is selected as pure components within the simulation basis manager. The next task is to assign a fluids package, which is used by the software to calculate the component streams as they change within the HYSYS flow sheet. The selection of the fluids package is critical. There are dangers of using an incorrect thermodynamics package. They state, “Everything from the energy balance to the volumetric flow rates to the separation in the equilibrium-stage units depends on accurate thermodynamic data”. For simulation of nitrogen liquefaction cycle, BWRS equation of state is used in this project work. 3.4 Equation of state In physics and thermodynamics, an equation of state is a relation between state variables. More specifically, an equation of state is a thermodynamic equation describing the state of matter under a given set of physical conditions. It is a constitutive equation which provides a 20 mathematical relationship between two or more state functions associated with the matter, such as its temperature, pressure, volume, or internal energy. Equations of state are useful in describing the properties of fluids, mixtures of fluids, solids, and even the interior of stars. Aspen HYSYS contain various property packages, but for simulation of Nitrogen liquefication cycle BWRS equation of state is used and for helium liquefication cycle peng-Robinson equation of state is used because it doesn‟t allow for helium gas. 3.4.1 Peng-Robinson: Peng-Robinson is a Cubic equation of state P= a= b = α = (1+(0.37464+1.54226ω – 0.26992 ω2) (1-Tr0.5))2 Tr = In polynomial form: A= 21 B= Z3 – (1-B) Z2 + (A-3B2-2B) Z - (AB-B2-B3) = 0 where, ω is the acentric factor of the species and R is the universal gas constant. The Peng-Robinson equation was developed in 1976 in order to satisfy the following goals: 1. The parameters should be expressible in terms of the critical properties and the acentric factor. 2. The model should provide reasonable accuracy near the critical point, particularly for calculations of the compressibility factor and liquid density. 3. The mixing rules should not employ more than a single binary interaction parameter, which should be independent of temperature pressure and composition. 4. The equation should be applicable to all calculations of all fluid properties in natural gas processes. For the most part the Peng-Robinson equation exhibits performance similar to the Soave equation, although it is generally superior in predicting the liquid densities of many materials, especially nonpolar ones. The departure functions of the Peng-Robinson equation are given on a separate article. 22 3.4.2 BWRS (Benedict-Webb-Rubin): BWRS is an non-cubic equation P = ρRT + ( B0RT-A0 - + - )ρ2 + (bRT – a - )ρ3 + (a + )ρ6 + (1+γρ2)exp(-γρ2) 3.5 Simulation Environment The Simulation environment contains the main flow sheet where you do the majority of your work (installing and defining streams, unit operations, columns and sub flow sheets). Before entering the Simulation environment, you must have a fluid package with selected components in the component list and a property package. Fig: 3.3 simulation environment 23 The flow sheet in Aspen HYSYS shows the various components and the material streams needed to bring about the liquefaction of the nitrogen gas. It consists of various apparatus(Object Palette) but few object which are in our use are as mixer, an isentropic compressor, a chiller, a LNG countercurrent heat exchanger, an isenthalpic J-T valve, a separator which performs flash separation operations and logical operation units Set, Spreadsheet and Recycle. 3.6 The components or the blocks or the equipments The description of the various components and the conditions at which they operate are described subsequently. 3.6.1 HYSYS object A. Mixer The Mixer operation combines two or more inlet streams to produce a single outlet stream. A complete heat and material balance is performed with the Mixer. That is, the one unknown temperature among the inlet and outlet streams is always calculated rigorously. If the properties of all the inlet streams to the Mixer are known (temperature, pressure, and composition), the properties of the outlet stream is calculated automatically since the composition, pressure, and enthalpy is known for that stream. 24 B. Compressor There are various type of compressor that are available in market but in Aspen Hysys option of isentropic centrifugal compressor is available. The Centrifugal Compressor operation is used to increase the pressure of an inlet gas stream with relative high capacities and low compression ratios. Depending on the information specified, the Centrifugal Compressor calculates either a stream property (pressure or temperature) or a compression efficiency. C. Cooler/Chiller The Cooler operations are one-sided heat exchangers. The inlet stream is cooled (or heated) to the required outlet conditions, and the energy stream absorbs (or provides) the enthalpy difference between the two streams. These operations are useful when you are interested only in how much energy is required to cool or heat a process stream with a utility, but you are not interested in the conditions of the utility itself. D. Heat Exchanger / LNG The LNG (Liquefied Natural Gas) exchanger model solves heat and material balances for multi-stream heat exchangers and heat exchanger networks. The solution method can handle a wide variety of specified and unknown variables. For the overall exchanger, you can specify various parameters, including heat leak/heat loss, UA or temperature approaches. Two solution approaches are employed; in the case of a single unknown, the solution is calculated directly from an energy balance. In the case of multiple unknowns, an iterative approach is used that 25 attempts to determine the solution that satisfies not only the energy balance, but also any constraints, such as temperature approach or UA. Heat Transfer Theory of LNG The LNG calculations are based on energy balances for the hot and cold fluids. The following general relation applies any layer in the LNG unit operation. where: m (hin –hout ) + Qinternal + Qexternal = ρ E. Separator Multiple feeds, one vapour and one liquid product stream. In Steady State mode, the Separator divides the vessel contents into its constituent vapour and liquid phases 3.6.2 Logical Units A. SET SET is used to set the value of a specific process variable (P V in the manuals) in relation to another PV. The relation must be of the form Y = mX + b and the process variables must be of the same type. For example, you could use the SET to set one material streams temperature to always be 20 degrees hotter than another material stream's temperature. SET may work both ways (i.e. if the target is known and not the source, the target will "set" the source). 26 B. SPREADSHEET The Spreadsheet applies the functionality of Spreadsheet programs to flowsheet modeling. With essentially complete access to all process variables, the Spreadsheet is extremely powerful and has many applications in HYSYS. The HYSYS Spreadsheet has standard row/column functionality. You can import a variable, or enter a number or formula anywhere in the spreadsheet. The Spreadsheet can be used to manipulate or perform custom calculations on flowsheet variables. Because it is an operation calculations are performed automatically; Spreadsheet cells are updated when flowsheet variables change. One application of the Spreadsheet is the calculation of pressure drop during dynamic operation of a Heat Exchanger. In the HYSYS Heat Exchanger, the pressure drop remains constant on both sides regardless of flow. However, using the Spreadsheet, the actual pressure drop on one or both sides of the exchanger could be calculated as a function of flow. Complex mathematical formulas can be created, using syntax which is similar to conventional Spreadsheets. Arithmetic, logarithmic, and trigonometric functions are examples of the mathematical functionality available in the Spreadsheet. The Spreadsheet also provides logical programming in addition to its comprehensive mathematical capabilities 27 C. RECYCLE Use this operation every time you need to recycle a stream. The logical block connects the two streams around the tear (remember the tear does not have to be the official "recycle" stream itself, but instead should be the best place in the loop to make the break for convergence purposes). Before you can install the REC YCLE the flow sheet must have completed. That means there need to be values for both the assumed stream and the calculated stream. Once the Recycle is attached and running, HYS YS compares the two values, adjusts the assumed stream, and runs the flow sheet again. HYSYS repeats this process until the two streams match within specified tolerances. Those tolerances are set on the Parameters Page. There are tolerances for Vapour Fraction, Temperature, Pressure, F low, Enthalpy, and Composition. The tolerances you enter are not absolute. They are actually multipliers for HYSYS' internal convergence tolerances. For example, the internal value for Temperature is .01 degrees (note that is in Kelvin, because HYSYS does all of its calculations in an internal unit set), so a multiplier often means the two streams must be within a tenth of a degree of each other. On the Numerical Page, among other things, you may set the RECYC LE to either Nested (the Op is called whenever it is encountered in the flow sheet) or Simultaneous (all of the RECYCLEs are invoked) 28 Chapter: 4 RESULT 29 4.1 Simulation of Linde cycle Problem specification: 1 To solve Linde cycle, (using ASPEN-HYSYS) as simulation tool. Given condition: Tambient = 300K, Pambient = 1 bar, Pmax = 100 bar, 150bar, 200bar, 250bar, 300bar, 350bar, 400bar, 450bar, 500bar, 550bar, 600bar Minimum temperature approach in HX= 10K, Pressure drop (except valve) is zero Fluid package = BWRS Fluid = pure nitrogen Fig: 4.1 PFD of Linde cycle 30 Pressure 100 150 200 250 300 350 Yield 1.89E-02 3.40E-02 4.22E-02 5.18E-02 5.65E-02 5.89E-02 Pressure 400 450 500 550 600 Yield 5.97E-02 5.91E-02 5.75E-02 5.48E-02 5.14E-02 Table: 4.1 variation of yield with pressure 7.00E-02 6.00E-02 Yeild (Kg/s) 5.00E-02 4.00E-02 3.00E-02 2.00E-02 1.00E-02 0.00E+00 0 100 200 300 400 500 Pressure ( bar ) Fig: 4.2 Yield vs pressure plot for linde system 31 600 700 Problem specification: 2 To solve Linde cycle, (using ASPEN-HYSYS) as simulation tool. Given condition: Tambient = 300K, Pambient = 1 bar, Pmax = 200bar Minimum temperature approach in HX= 0 K to 50K, Pressure drop (except valve) is zero Fluid package = BWRS Fluid = pure nitrogen Min approach (k) 0 3 5 10 15 20 25 29 Yeild (%) 6.68E-02 6.02E-02 5.59E-02 4.47E-02 3.31E-02 2.12E-02 9.26E-03 0.00 Table: 4.2 variation of yield with minimum approach of heat exchanger 8.00E-02 7.00E-02 6.00E-02 yeild(%) 5.00E-02 4.00E-02 3.00E-02 2.00E-02 1.00E-02 0.00E+00 0 5 10 15 20 25 minimum approch(K) Fig: 4.3 variation of yield with minimum approach of heat exchanger 32 30 35 4.1.1 Figure of merit: FOM for linde cycle is given as : FOM = * Case- 1: FOM for minimum approach of 0 K FOM = * = = * * = 0.11 Case- 2: FOM for minimum approach of 10 K FOM = = * * = 0.07689 33 4.2 Simulation of Claude cycle Problem specification: 3 To solve Claude cycle, (using ASPEN-HYSYS) as simulation tool to find the value of x the minimum work required to liquefy a unit mass of nitrogen Given condition: Tambient = 300K, Pambient = 1.1 bar, Pmax = 8 bar, Minimum temperature approach in HX1= 3K, HX2= 2K, HX3= 1K Pressure drop in heat exchange is 0.1 bars in each stream is zero Fluid package = BWRS Fluid = pure nitrogen Efficiency of turbine = 40 % Fig: 4.4 Claude PFD 34 Wcomp Wchiller Wturbine (KW) (KW) (KW) 313 311.4 313 χ Wnet (KW) Y Wnet /Y 3.849 0.1 309.151 5.46E-03 56613 311.4 6.065 0.2 306.935 1.05E-02 29331 313 311.4 7.842 0.3 305.158 1.42E-02 21561 313 311.4 9.167 0.4 303.833 1.76E-02 17284 313 311.5 10.25 0.5 302.75 2.01E-02 15029 313 311.5 11.33 0.6 301.67 2.26E-02 13371 313 311.5 12.94 0.7 300.06 2.65E-02 11334 313 311.5 14.58 0.8 298.42 2.99E-02 9979 313 311.5 16.2 0.9 296.8 3.37E-02 8809 313 311.6 16.53 0.92 296.47 3.45E-02 8604 313 311.6 16.69 0.93 296.31 3.49E-02 8494 313 311.6 16.85 0.94 296.15 3.54E-02 8354 313.1 311.6 17.02 0.95 296.08 3.58E-02 8260 313 311.6 16.61 0.96 296.39 3.49E-02 8501 Table: 4.3 Net works required to liquefy nitrogen at different value of x without effectiveness 35 60000 Wnet/Y 50000 40000 30000 20000 10000 0 0 0.2 0.4 0.6 0.8 1 1.2 X (a) 8900 8800 Wnet/Y 8700 8600 8500 8400 8300 8200 0.89 0.9 0.91 0.92 0.93 0.94 0.95 0.96 0.97 X (b) Fig: 4.5 Work required liquefying a unit mass of nitrogen in the Claude system (a) Full plot , (b) magnify plot 36 (a) (b) (c) Fig: 4.6 Temperature profile in heat exchanger at optimum value (a) First HX (b) second HX (c) third HX 37 Problem specification:4 To solve Claude cycle, (using ASPEN-HYSYS) as simulation tool to find the value of x where minimum work required to liquefy a unit mass of nitrogen Given condition: Tambient = 300K, Pambient = 1.1 bar, Pmax = 8 bar, Minimum temperature approach in, HX2= 2K, HX3= 1K Effectiveness in heat exchanger1 = 0.99 Pressure drop in heat exchange is 0.1 bars in each stream is zero Fluid package = BWRS Fluid = pure nitrogen Efficiency of turbine = 40 % Fig: 4.7 Claude PFD with effectiveness in first HX 38 Wcomp Wchiller Wturbine (KW) (KW) (KW) 313.7 312.9 313.3 χ Wnet (KW) Y Wnet /Y 3.608 0.1 310.092 6.24E-03 49730 312.1 5.934 0.2 307.366 1.07E-02 28739 313.1 311.6 7.679 0.3 305.421 1.46E-02 20958 312.9 311.9 9.094 0.4 303.806 1.74E-02 17488 312.8 311 10.21 0.5 302.59 1.97E-02 15370 312.7 310.8 11.26 0.6 301.44 2.15E-02 14007 312.6 310.7 12.86 0.7 299.74 2.53E-02 11836 312.6 310.7 14.47 0.8 298.13 2.91E-02 10233 312.6 310.7 16.1 0.9 296.5 3.25E-02 9116 312.6 310.7 16.58 0.93 296.02 3.39E-02 8738 312.6 310.7 16.74 0.94 295.86 3.43E-02 8636 312.6 310.7 16.9 0.95 295.7 3.47E-02 8533 312.6 310.6 16.77 0.96 295.83 3.40E-02 8711 Table: 4.4 Net works required to liquefy nitrogen at different value of x with effectiveness 39 60000 50000 Wnet/Y 40000 30000 20000 10000 0 0 0.2 0.4 0.6 0.8 1 1.2 X (a) 9200 9100 Wnet/Y 9000 8900 8800 8700 8600 8500 0.89 0.9 0.91 0.92 0.93 0.94 0.95 0.96 0.97 X (b) Fig: 4.8 Optimum work required liquefying a unit mass of nitrogen in the Claude system (a) Full plot , (b) magnify plot 40 Stream Heat Exchanger 1 Heat Exchanger 2 Inlet Temp Outlet Temp Inlet Temp Outlet Temp Hot 300 234.9873817 234.98738 Cold 230.74357 297.0000374 Hot 300 Cold Heat Exchanger 3 Inlet Temp Outlet Temp 205.9133847 205.9134 99.98329836 203.91339 230.7448434 80.47354 204.9133785 187.3291029 187.3291 160.0016677 160.0017 99.98144135 180.955608 297.0000094 158.0017 180.9626182 80.4751 159.001674 Hot 300 162.5113138 162.51131 136.6633889 136.6634 99.97988856 Cold 154.184043 297.0000084 134.66339 154.1590752 80.47787 135.6633934 Hot 300 145.4887875 145.48879 120.9300694 120.9301 99.98121968 Cold 135.290818 297.0000094 118.93013 135.2908181 80.47548 119.9300976 Hot 300 132.4287429 132.42874 108.6749137 108.6749 99.98286489 Cold 120.376241 297.0000092 106.67491 120.3839175 80.47557 107.6749112 Hot 300 123.045602 123.0456 100.1715691 100.1699 99.98172878 Cold 109.237594 297.000013 97.817001 109.2201367 80.47701 99.16990122 Hot 300 120.6106759 120.55241 100.1692879 100.1724 99.98317238 Cold 105.634559 296.9999948 95.859474 105.6462591 80.47463 99.17244586 Hot 300 118.7951288 118.86473 100.1713003 100.1703 99.9814977 Cold 102.833055 296.9999937 94.013849 102.8272339 80.47565 99.17025042 Hot 300 117.397003 117.4815 100.1684378 100.1681 99.98197968 Cold 100.41723 296.9999835 92.086632 100.4349266 80.47534 99.16810968 Hot 300 117.1572037 117.24192 100.1721626 100.1709 99.9823053 Cold 99.9907895 297.0000659 91.701077 99.99891265 80.47624 99.17094508 Hot 300 117.0580251 117.1267 100.1683684 100.1691 99.98173797 Cold 99.7919159 297.0001304 91.510632 99.78421232 80.47505 99.1691329 Hot 300 116.9583199 116.95832 100.17144 100.1694 99.98222408 Cold 99.5655898 297 91.260588 99.56968262 80.47504 99.16941655 Hot 300 116.8946362 116.89464 100.1717553 100.1699 99.98159411 Cold 99.3743943 297.000008 91.061583 99.36409725 80.47577 99.16983826 Hot 300 112.7289117 112.72891 88.84143951 88.84144 88.44846541 Cold 94.5922938 297.0000087 86.841458 94.59229383 80.47536 87.84143917 Table: 4.5 Temperature across heat exchanger at different value of x 41 χ 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.92 0.93 0.94 0.95 0.96 For low pressure Claude system we can see from above table it can be seen that at optimum valve (0.95) temperature drop in hot stream of cold heat exchanger is 0.39297K (negligible) and temperature increase in cold stream is 18.694K. So third heat exchanger or low temperature heat exchanger of Claude system if neglected it not cause any appreciable difference in output of Claude system at optimum operating condition. This modified Claude system with two (first and second) heat exchanger system is known as kapitza system. 4.3 Simulation of Kapitza cycle Problem specification: 5 To solve kapitza system, (using ASPEN-HYSYS) as simulation tool to find the value of x where minimum work required to liquefy a unit mass of nitrogen Given condition: Tambient = 300K, Pambient = 1.1 bar, Pmax = 8 bar, Minimum temperature approach in HX1= 3K, HX2= 2K, Pressure drop in heat exchange is 0.1 bars in each stream is zero Fluid package = BWRS Fluid = pure nitrogen Efficiency of turbine = 40 % 42 Fig: 4.9 Kapitza PFD Wcomp (KW) Wchiller (KW) Wturbine (KW) χ Wnet (KW) Y Wnet /Y 313 311.4 3.245 0.1 309.755 3.79E-03 81671 313 311.4 5.119 0.2 307.881 8.22E-03 37463 313 311.4 6.669 0.3 306.331 1.16E-02 26393 313 311.4 8.195 0.4 304.805 1.51E-02 20137 313 311.5 9.763 0.5 303.237 1.87E-02 16215 313 311.5 11.35 0.6 301.65 2.25E-02 13419 313 311.5 12.95 0.7 300.05 2.62E-02 11449 313 311.5 14.56 0.8 298.44 3.01E-02 9916 313 311.5 16.2 0.9 296.8 3.36E-02 8837 313 311.6 16.53 0.92 296.47 3.41E-02 8698 313 311.6 16.4 0.94 296.6 3.53E-02 8403 313 311.6 17 0.95 296 3.58E-02 8267 313 311.6 16.54 0.96 296.46 3.45E-02 8595 Table: 4.6 Net works required to liquefy nitrogen at different value of x for kapitza system 43 90000 80000 70000 Wnet/Y 60000 50000 40000 30000 20000 10000 0 0 0.2 0.4 0.6 0.8 1 1.2 X (a) 8900 8800 Wnet/Y 8700 8600 8500 8400 8300 8200 0.89 0.9 0.91 0.92 0.93 0.94 0.95 0.96 0.97 X (b) Fig: 4.10 Optimum work required liquefying a unit mass of nitrogen in the Kapitza system (a) Full plot , (b) magnify plot 44 If we compare Claude Table 4.2 and kapitza Table 4.5 we can see that at initial or when mass flow through turbine is less work required to liquefy unit mass of nitrogen is more in kapitza system (two heat exchange system) as compare to Claude system (three heat exchanger) while it can be observed that at optimum value work required to liquefy unit mass is almost same as of Claude system as well as optimum value is also same. It can be seen in overlap plot for kapitza and Claude net work require to liquefy nitrogen 8900 kapitza 8800 Wnet/Y 8700 Claude 8600 8500 8400 8300 8200 0.89 0.9 0.91 0.92 0.93 0.94 0.95 X Fig: 4.11 comparison of work required to liquefy unit mass of nitrogen 45 0.96 0.97 4.4 Simulation of Claude cycle for Haylent Problem specification: 6 To solve Claude system, (using ASPEN-HYSYS) as simulation tool to find the value of x where minimum work required to liquefy a unit mass of nitrogen Given condition: Tambient = 300K, Pambient = 1.1 bar, Pmax = 150 bar, Minimum temperature approach in HX1= 3K, HX2= 2K, HX3= 1K Pressure drop in heat exchange is 0.1 bars in each stream is zero Fluid package = BWRS Fluid = pure nitrogen Efficiency of turbine = 70 % Wchiller Wturbine χ Wcomp (KW) Wnet Y Wnet /Y (KW) (KW) (KW) 1247 1270 29.71 0.2 1217.29 0.122327 9951 1247 1270 44.56 0.3 1202.44 0.156666 7675 1248 1270 58.41 0.4 1189.59 0.18643 6380 1248 1271 69.39 0.5 1178.61 0.212245 5553 1248 1271 78.16 0.6 1169.84 0.23242 5033 1248 1271 78.89 0.61 1169.11 0.234236 4991 1248 1271 79.52 0.62 1168.48 0.232441 5027 Table: 4.7 Net works required to liquefy nitrogen at different value of x for Claude system 46 5040 5035 5030 5025 Wnet/Y 5020 5015 5010 5005 5000 4995 4990 4985 0.595 0.6 0.605 0.61 0.615 0.62 0.625 X Fig: 4.12 Optimum work required liquefying a unit mass of nitrogen in the claude system 4.5 Simulation of Haylent system Problem specification: 7 To solve Claude system, (using ASPEN-HYSYS) as simulation tool to find the value of x where minimum work required to liquefy a unit mass of nitrogen Given condition: Tambient = 300K, Pambient = 1.1 bar, Pmax = 150 bar, Minimum temperature approach in HX2= 2K, HX3= 1K Pressure drop in heat exchange is 0.1 bars in each stream is zero Fluid package = BWRS Fluid = pure nitrogen Efficiency of turbine = 70 % 47 Fig: 4.13 Haylent PFD Wchiller Wturbine (KW) (KW) 1212 1235 29.72 0.2 1212 1236 44.58 1202 1222 1170 Wcomp (KW) χ Wnet Y Wnet /Y 1182.28 0.122264 9669 0.3 1167.42 0.156643 7452 59.4 0.4 1142.6 0.184114 6205 1182 74.3 0.5 1095.7 0.198412 5522 1147 1152 81.73 0.55 1065.27 0.200576 5311 1116 1113 89.16 0.6 1026.84 0.198115 5183 1101 1093 92.13 0.62 1008.87 0.195474 5161 1092 1083 93.62 0.63 998.38 0.193757 5152 1081 10.68 95.1 0.64 985.9 0.190023 5188 1067 1051 96.59 0.65 970.41 0.184731 5253 997.3 962 104 0.7 893.3 0.158495 5636 (KW) Table: 4.8 Net works required to liquefy nitrogen at different value of x for Haylent system 48 5190 5185 5180 Wnet/Y 5175 5170 5165 5160 5155 5150 5145 0.595 0.6 0.605 0.61 0.615 0.62 0.625 0.63 0.635 0.64 0.645 X Fig: 4.14 Optimum work required liquefying a unit mass of nitrogen in the Haylent system 49 Chapter: 5 Simulation of LN2 liquefication plant at NIT-Rourkela 50 5.1 LN2 plant at NIT-Rourkela A future plan at cryogenic centre at NIT-Rourkela is to setup a second nitrogen liquefication plant which produce liquid nitrogen whose working principal is based on Kapitza cycle. Fig: 5.1 LN2 plant PFD Simulation of LN2 system Problem specification: To solve LN2 system, (using ASPEN-HYSYS) as simulation tool to find the value of x where minimum work required to liquefy a unit mass of nitrogen Given condition: Tambient = 310K, Pambient = 1.1 bar, Pmax = 8 bar, Effectiveness of HX1= 0.9, 0.95, 0.97, 0.98, 1.0 Minimum temperature approach in HX2= 0.5K, 1.0K, 2.0K Pressure drop in heat exchange is 0.1 bars in each stream is zero Fluid package = BWRS Fluid = pure nitrogen Efficiency of turbine = 40 %, 50 %, 60 %, 70 %, 100 % 51 % of S.No ηturbine ε HX1 ∆T HX2 Yield (Kg/s) Wcomp/Y yeild Kwh/lit 1 40 100 0.5 4.16E-03 8662 3.99 19.17 2 40 100 1 4.08E-03 8822 3.915 19.52 3 40 100 2 4.11E-03 8766 3.944 19.39 4 40 98 0.5 3.21E-03 10765 3.08 23.82 5 40 98 1 3.23E-03 10987 3.099 24.31 6 40 98 2 3.20E-03 11101 3.071 24.56 7 40 97 0.5 2.80E-03 12612 2.687 27.91 8 40 97 1 2.78E-03 12679 2.667 28.05 9 40 97 2 2.81E-03 12578 2.686 27.83 10 40 95 0.5 1.95E-03 17861 1.871 39.52 11 40 95 1 1.92E-03 18185 1.369 40.24 12 40 95 2 1.91E-03 18222 1.362 40.32 13 40 90 0.5 0 0 0 0 14 40 90 1 0 0 0 0 15 40 90 2 0 0 0 0 16 50 100 0.5 5.22E-03 6898 3.723 15.26 17 50 100 1 5.17E-03 6965 3.687 15.41 18 50 100 2 5.15E-03 6989 3.673 15.46 19 50 98 0.5 4.36E-03 8257 3.1098 18.27 20 50 98 1 4.33E-03 8202 3.088 18.15 21 50 98 2 4.31E-03 8242 3.074 18.24 22 50 97 0.5 3.95E-03 8935 2.817 19.77 23 50 97 1 3.93E-03 8997 3.771 19.91 24 50 97 2 3.91E-03 9037 3.752 19.99 25 50 95 0.5 3.15E-03 11057 3.023 24.47 52 yield S.No ηturbine ε HX1 ∆T HX2 26 50 95 1 27 50 95 28 50 29 (Kg/s) Wcomp/Y % of yeild Kwh/lit 3.08E-03 11305 2.955 25.01 2 3.06E-03 11393 2.936 25.21 90 0.5 1.00E-03 33522 0.959 74.18 50 90 1 9.48E-04 35508 0.909 78.18 30 50 90 2 8.57E-04 39265 0.822 86.89 31 60 100 0.5 6.31E-03 5707 6.055 12.62 32 60 100 1 6.29E-03 5720 6.036 12.65 33 60 100 2 6.23E-03 5778 5.978 12.78 34 60 98 0.5 5.49E-03 6477 5.268 14.33 35 60 98 1 5.46E-03 6515 5.239 14.41 36 60 98 2 5.39E-03 6589 5.182 14.58 37 60 97 0.5 5.12E-03 6899 4.93 15.26 38 60 97 1 5.11E-03 6911 4.9 15.29 39 60 97 2 5.04E-03 7012 4.836 15.51 40 60 95 0.5 4.29E-03 8067 4.117 17.85 41 60 95 1 4.27E-03 8134 4.097 18.00 42 60 95 2 4.24E-03 8226 4.069 18.2 43 60 90 0.5 2.31E-03 14588 2.21 32.28 44 60 90 1 2.30E-03 14652 2.2 32.42 45 60 90 2 2.24E-03 15038 2.149 33.28 46 70 100 0.5 7.43E-03 4843 7.13 10.71 47 70 100 1 7.40E-03 4865 7.1 10.76 48 70 100 2 7.33E-03 4910 7.034 10.86 49 70 98 0.5 6.65E-03 5345 6.381 11.82 50 70 98 1 6.61E-03 5377 6.343 11.89 53 yield % of S.No ηturbine ε HX1 ∆T HX2 (Kg/s) Wcomp/Y yeild Kwh/lit 51 70 98 2 6.55E-03 5434 6.285 12.02 52 70 97 0.5 6.34E-03 5577 6.084 12.34 53 70 97 1 6.22E-03 5678 5.969 12.56 54 70 97 2 6.21E-03 5692 5.959 12.59 55 70 95 0.5 5.55E-03 6288 5.32 13.91 56 70 95 1 5.51E-03 6332 5.287 14.01 57 70 95 2 5.41E-03 6446 5.191 14.26 58 70 90 0.5 3.70E-03 9129 3.55 20.20 59 70 90 1 3.60E-03 9366 3.454 20.72 60 70 90 2 3.43E-03 9558 3.291 21.15 61 100 100 0.5 1.11E-02 3248 10.65 7.18 62 100 100 1 1.10E-02 3271 10.55 7.23 63 100 100 2 1.09E-02 3312 10.46 7.33 64 100 98 0.5 1.04E-02 3407 9.98 7.53 65 100 98 1 1.04E-02 3426 9.98 7.58 66 100 98 2 1.01E-02 3510 9.692 7.76 67 100 97 0.5 1.02E-02 3475 9.788 7.69 68 100 97 1 1.01E-02 3509 9.692 7.76 69 100 97 2 9.99E-03 3542 9.587 7.83 70 100 95 0.5 9.47E-03 3692 9.088 8.17 71 100 95 1 9.50E-03 3678 9.11 8.14 72 100 95 2 9.40E-03 3719 9.021 8.23 73 100 90 0.5 7.99E-03 4241 7.667 9.38 74 100 90 1 7.91E-03 4282 7.591 9.47 75 100 90 2 7.77E-03 4356 7.456 9.63 Table: 5.1 Optimum work required at various combination of efficiency of turbine, minimum approach and effectiveness of heat exchange of LN2 plant 54 Chapter: 6 Conclusion 55 Conclusion The above project work presents a cycle simulation for the Nitrogen liquefaction cycle with a compressor, heat exchanger and a J-T valve. It gives us the design data in terms of nodal temperature across the heat exchanger, compressor, chiller etc. and mass flow rates through all the equipments. The above simulation work for Claude‟s liquefaction cycle for Nitrogen eliminate time and cost expenditure by successfully proven that for low working pressure for Claude system it is useless to use last or low temperature heat exchanger as well as for high working pressure of Claude cycle first heat exchanger is worth. The simulation can be adapted to bring about any changes in the configuration of the liquefaction cycle and can be successfully applied for other complicated cycle. 56 References 1) Randall F Barron, „Cryogenic Systems‟, second edition , New York, Oxford University Press, 1985 2) Flynn Thomas M., „Cryogenic Engineering‟, Colorado, Oxford University Press, 1992. 3) Steven W. Van Sciver, “Helium cryogenics” , New York , Pentium publishing corporation , 1986 4) AspenONE 2006 Documentation- provided with licenses package of AspenONE 2006. 5) Rice university: http://www.rice.edu/ 57

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