LPG by Deniz - EGE UNIVERSITY CHEMICAL ENGINEERING...

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Unformatted text preview: EGE UNIVERSITY CHEMICAL ENGINEERING DEPARTMENT Che220 CONCEPTUAL DESIGN I LPG PRODUCTİON AND STORAGE Preparated by group XIII: 05‐06‐8049 Deniz MUTLU 05‐06‐8081 Zeynep AKGÜN 05‐06‐8083 Başar YILMAZ 05‐06‐8050 Süheyl SÜMBÜLTEPE Submitted to: Prof. Dr. Firuz Balkan May 2009 Bornova, IZMIR TABLE OF CONTENTS 1.0 Introduction......................................................................................................................ii 2.0 Summary...........................................................................................................................ii 3.0 Aim......................................................................................................................................1 4.0 Why LPG?..........................................................................................................................1 5.0Field of use LPG…………………………………………………………………………………………………………..3 5.1 As motor fuel...........................................................................................................3 5.2 As refrigerant...........................................................................................................3 5.2.1 In motor vehicles............................................................................................4 5.3 As cooking fuel........................................................................................................4 5.4 Comparison to natural gas......................................................................................5 6.0 Discussion........................................................................................................................5 7.0 Nomenclature..................................................................................................................7 8.0 References.......................................................................................................................8 9.0 Appendix..........................................................................................................................10 9.1 Appendix A.............................................................................................................10 9.2 Appendix B.............................................................................................................17 i 1.0 Introduction Liquefied petroleum gas (also called LPG, GPL, LP Gas, or autogas) is a mixture of hydrocarbon gases used as a fuel in heating appliances and vehicles, and increasingly replacing chlorofluorocarbons as an aerosol propellant and a refrigerant to reduce damage to the ozone layer. Varieties of LPG bought and sold include mixes that are primarily propane, mixes that are primarily butane, and the more common, mixes including both propane (60%) and butane (40%), depending on the season—in winter more propane, in summer more butane. Propylene and butylenes are usually also present in small concentration. A powerful odorant, ethanethiol, is added so that leaks can be detected easily. LPG is synthesised by refining petroleum or 'wet' natural gas, and is usually derived from fossil fuel sources, being manufactured during the refining of crude oil, or extracted from oil or gas streams as they emerge from the ground. It was first produced in 1910 by Dr. Walter Snelling, and the first commercial products appeared in 1912. It currently provides about 3% of the energy consumed, and burns cleanly with no soot and very few sulfur emissions, posingno ground or water pollution hazards.However, its energy density per unit volume is lower than either petrol or diesel. At normal temperatures and pressures, LPG will evaporate. Because of this, LPG is supplied in pressurised steel bottles. In order to allow for thermal expansion of the contained liquid, these bottles are not filled completely; typically, they are filled to between 80% and 85% of their capacity. The ratio between the volumes of the vaporised gas and the liquefied gas varies depending on composition, pressure and temperature, but is typically around 250:1. The pressure at which LPG becomes liquid, called its vapour pressure, likewise varies depending on composition and temperature; LPG is heavier than air, and thus will flow along floors and tend to settle in low spots, such as basements. This can cause ignition or suffocation hazards if not dealt with. Large amounts of LPG can be stored in bulk tanks and can be buried underground if required. Alternatively, gas cylinders can be used. 2.0 Summary LPG liquefaction process is going to investigate in this report.Beside the cycle of this process will be presented in Theory and Principle part; the enthalpy, work, heat and thickness calculations will be shown in Appendix section. ii 3.0 Aim The aim of this process is liquefied the 31 ton gas and storage it into a spherical tank. For this process we use the mixture of propane and n‐butane gases. All calculations were made for this amount. 4.0 Why LPG? The world is changing and everyday scientists are developing new sources for human life. Well changing world conditions why we use LPG beside of other energy sources. Because LPG ; • • • Clean LPG: The environmentally friendly alternative LPG is one of the cleanest energy sources, in terms of transport, storage and end‐use. Associated CO2 emissions are considerably less than those of most other fossil fuels. Furthermore, LPG emits almost no NOx (nitrogen oxide), SOx (sulphur oxide) or PM • • • • • • (particulate matters). These characteristics allow LPG to contribute not only to fighting climate change but also to environmental protection in general and the improvement of indoor and outdoor air quality in particular. Healthy LPG: The energy that doesn’t compromise human health LPG’s physico‐chemical characteristics make it a clean energy that can facilitate growth and development without posing a threat to human beings. Generating fewer CO2 emissions than other fossil fuels and only trace amounts of NOx (nitrogen oxide), SOx (sulphur oxide) and PM (particulate matters), the combustion of LPG has no harmful effects on human health. Multi‐purpose 1 LPG: Take it anywhere – Use it for anything Whether used for cooking, space and water‐heating or automotive fuel, LPG is a highly flexible and immediately available solution to the energy needs of European citizens. • Thanks to a wide range of packaging and storage options (cartridges, refillable cylinders from 2 kg to 45 kg bulk tanks placed above or below ground, etc …), LPG is suitable for a multitude of applications. • Portable • LPG: The power of portable energy • With its high volume‐to‐energy‐yield ratio and flexibility in terms of packaging and storage, LPG can be transported, stored and used effectively anywhere on earth. • Easily converted into liquid form, LPG can be delivered can be transported inbulk form in large tanks, carried by rail, by road or by sea. Alternatively, it can be delivered to end‐ users in individual cylinders by truck. • LPG can thus be distributed in cities, industrial zones, and low‐density residential areas as well as in remote rural regions (mountains, islands, etc…). • The wide reach of LPG’s distribution network makes it an ideal complement to the natural gas (methane) grid. • It can rapidly be put into action in the aftermath of natural disasters and humanitarian crises requiring local availability of energy for heating, cooking or power generation. • Efficient • LPG: Towards a more energy‐efficient Europe • With a high calorific value (47.3 Tj/Gg), LPG is among the most efficient fuels available. Its use reduces waste and helps lessen the strain of energy use on the natural environment. • Furthermore, due to their direct and frequent contact with end‐users, LPG distributors are well‐placed to inform and educate citizens about strategies for achieving more efficient energy use. • Strategic • LPG: A strategic energy choice for Europe There are no concerns as to the availability of LPG in the foreseeable future. LPG can therefore play an ongoing role in Europe’s energy portfolio both now and in the future, enhancing security of supply by contributing to diversification. • LPG enjoys the advantages of multiple origins, numerous entry‐points into Europe and a highly flexible supply chain. Vulnerability to supply disruption is further reduced by the absence of pipe networks. 2 • • 5.0 Field of use LPG 5.1 As motor fuel Main article: Autogas When LPG is used to fuel internal combustion engines, it is often referred to as autogas or auto propane. In some countries, it has been used since the 1940s as an alternative fuel for spark ignition engines. More recently, it has also been used in diesel engines. Its advantage is that it is non‐toxic, non‐corrosive and free of tetra‐ethyl lead or any additives, and has a high octane rating (108 RON). It burns more cleanly than petrol or diesel and is especially free of the particulates from the latter. LPG has a lower energy density than either petrol or diesel, so the equivalent fuel consumption is higher. Many governments impose less tax on LPG than on petrol or diesel, which helps offset the greater consumption of LPG than of petrol or diesel. 5.2 As refrigerant LPG is instrumental in providing off‐the‐grid refrigeration, usually by means of a gas absorption refrigerator. Blends of pure, dry "isopropane" (refrigerant designator R‐290a ) and isobutane (R‐600a) have negligible Ozone depletion potential and very low Global Warming Potential and can serve as a functional replacement for R‐12, R‐22, R‐134a, and other chlorofluorocarbon or hydrofluorocarbon refrigerants in conventional stationary refrigeration and air conditioning systems. 3 5.2.1 In motor vehicles Such substitution is widely prohibited or discouraged in motor vehicle air conditioning systems, on the grounds that using flammable hydrocarbons in systems originally designed to carry non‐flammable refrigerant presents a significant risk of fire or explosion. Vendors and advocates of hydrocarbon refrigerants argue against such bans on the grounds that there have been very few such incidents relative to the number of vehicle air conditioning systems filled with hydrocarbons. One particular test was conducted by a professor at the University of New South Wales that unintentionaly tested the worst case scenario of a sudden and complete refrigerant loss into the passenger compartment followed by subsequent ignition. He and several others in the car sustained burns to their face, ears, and hands, and several observers received lacerations from the burst glass of the front passenger window. 5.3 As cooking fuel Truck carrying LPG cylinders to residential consumers in Singapore According to the 2001 Census of India, 17.5% of Indian households or 33.6 million Indian households used LPG as cooking fuel in 2001.[14] 76.64% of such households were from 4 urban India making up 48% of urban Indian households as compared to a usage of 5.7% only in rural Indian households. LPG is subsidised by the government. Increase in LPG prices has been a politically sensitive matter in India as it potentially affects the urban middle class voting pattern. LPG was once a popular cooking fuel in Hong Kong; however, the continued expansion of town gas to buildings has reduced LPG usage to less than 24% of residential units. LPG is the most common cooking fuel in Brazilian urban areas, being used in virtually all households. Poor families receive a government grant ("Vale Gás") used exclusively for the acquisition of LPG. 5.4 Comparison to natural gas LPG has a higher calorific value (94 MJ/m3 equivalent to 26.1kWh/m³) than natural gas (methane) (38 MJ/m3 equivalent to 10.6 kWh/m3), which means that LPG cannot simply be substituted for natural gas. In order to allow the use of the same burner controls and to provide for similar combustion characteristics, LPG can be mixed with air to produce a synthetic natural gas (SNG) that can be easily substituted. LPG/air mixing ratios average 60/40, though this is widely variable based on the gases making up the LPG. The method for determining the mixing ratios is by calculating the Wobbe index of the mix. Gases having the same Wobbe index are held to be interchangeable. LPG‐based SNG is used in emergency backup systems for many public, industrial, and military installations, and many utilities use LPG peak shaving plants in times of high demand to make up shortages in natural gas supplied to their distributions systems. LPG‐SNG installations are also used during initial gas system introductions, when the distribution infrastructure is in place before gas supplies can be connected. Developing markets in India and China (among others) use LPG‐SNG systems to build up customer bases prior to expanding existing natutral gas systems. 6.0 Discussion As accorded in AIM, this project is prepared for liquefied 23 ton propane and butane gas mixture by using Linde Liquefaction Process. The whole process calculation are made by assuming the process is reversible and adiabatic with the other assumptions such as ideal gas mixture properties. A reversible process: • • Is frictionless Is never more than differentially removed from equilibrium 5 • • • Traverses a succession of equilibrium states. Is driven by forces whose imbalance is differential in magnitude. Can be reversed at any point by a differential change in external conditions. However; If irreversible processes are considered, finite changes are made; therefore the system is not at equilibrium throughout the process. At the same point in an irreversible cycle, the system will be in the same state, but the surroundings are permanently changed after each cycle. Because of the assumption that the process is reversible, some calculations are different from the real process calculations. From the first process to process “A”, calculations are made according to isentropic compression (adiabatic+reversible) process. But in real process a change must be occur in entropy because of irreversibilities. Thus, work and HA must be different from the calculated values. This reason leads the temperature of B to be too lower than the feasible temperature. Additionally, the process between the point B and 2 is accepted as direct expansion, not “throttling”. Actually, a turbine can be add to this process to gain some energy from the produces work. But, since it complicate the process, it cannot be preferred. Another reason of these differences can be the assumption which shows the mixture is ideal. Even though the matters (propane and butane) are similar; they have some dissimilarity in mixture for example in pressure and temperature calculations. In addition to this reasons; the estimations are made with the superheated and saturation table of propane and butane. Unfortunately, there is doubt of correctitude of the saturated and superheated tables. It can be prepared for different basis value of temperature and pressure. Also we assumed ideal this process and cause of not reach suitable table variables that we have a nonacceptable TB . 6 7.0 Nomenclature P H Q W Hv Hl 0 Pressure [Pa] Enthalpy [J/mol, Btu/Ibm] Heat [ Work[ Enthalpy of vapor Enthalpy of liquid temperature, celcius energy, joule Temperature Ideal gas constant mol Specific heat temperature, celcius Volume Critical temperature Critical pressure Saturated Pressure Mass Entropy Molecular weight Weight fraction Joint efficiency Corrosion allowance Inside radius of tank Antoine Constant C J T R N Cp 0 C V Tc Pc Psat M S MW X E CA R A,B,C,D 7 8.0 Refernces • http://www.aegpl.eu/Content/Default.asp?PageID=71 • http://en.wikipedia.org/wiki/Liquefied_petroleum_gas • Perry's chemical engineering handbook • http://www.lpgwatch.co.uk/forum/ • http://www.worldlpgas.com/what‐is‐lp‐gas 8 9.0Appendix 9.1 APPENDIX A T Q ( P = cst ) A B ( H = cst ) Ws 20oC 2 (Saturated Liquid) 1 (Superheated Region) (P = 1 bar) S 9 Antoine constants, Tc, Pc propane n‐butane A 6.80398 6.80896 B 803.810 935.860 Antoine Equation is; In the beginning, we have %40 butane and %60 propane gas mixture,so we have to calculate Pc(mixture). log P sat = A − B [mm Hg] T in oC T +C C 246.99 238.730 TC [K] 369.8 425.1 PC [bar] 42.48 37.96 xb * Pcb + x p * Pc p = Pcmix Pc mix = 0.4 * 37.96 + 0.6 * 42.48 = 40.672bar Our new critical mixture pressure is 40.672 bar we have to assume PA.According to T‐ S diagram this pressure must be over the critical pressure of mixture.We assume 42 bar Pcmix = 42 bar. Psat of the gases at 20 oC; Pp sat 1 atm=1.01325 bar = 10 803.810 ⎞ ⎛ ⎜ 6.80398 − ⎟ 20 + 246.99 ⎠ ⎝ = 6213.6mmHg = 8.176atm = 8.284bar Pb sat = 10 935.860 ⎞ ⎛ ⎜ 6.80896 − ⎟ 20 + 238.730 ⎠ ⎝ = 155.36mmHg = 2.046atm = 2.073bar xb * Pb sat + x p * Pp sat = Pmix sat 0.4 * 2.046 + 0.6 * 8.176 = 5.724atm = 5.8bar 1 0 Betwen the point 1 ‐ A T Q ( P = cst ) A SA B ( H = cst ) Ws 20oC 2 (Saturated Liquid) 1 (P = 1 bar) (Superheated Region) S1 S Between the points 1‐A We have this section isentropic compression process= Adiabatic + Reversible. So S1= SA ∆S=0 We assume our gas mixture is ideal so we can use this equation; ∆S = Cp * ln P TA − R * ln A P1 T1 1 1 Cp [J/ mol.K] Molecular Weight(kg/kmol) Propane 74.834 58.123 n‐butane 99.169 44.097 Cpmix = xb * Cpb + x p * Cp p 0 = 84.568 * ln Cp mix = 0.4 * 99.169 + 0.6 * 74.834 = 84.568 J / mol.K TA 42 − 8.314 * ln 273.15 + 20 1 TA=423.324 K =150.174 Celcius=302.31 F As you see we are adding the system WS (in the graph) along this compression section.We can calculate WS by this equation; W( iso ) ⎡⎛ 42 ⎞ 8.314 / 84.568 ⎤ = 84.568 * 293.15⎢⎜ ⎟ − 1⎥ = 11008.632kJ / kmol ⎢⎝ 1 ⎠ ⎥ ⎣ ⎦ ⎡⎛ P = Cp * T1 ⎢⎜ 2 ⎜ ⎢⎝ P1 ⎣ ⎞ ⎟ ⎟ ⎠ R / Cp ⎤ − 1⎥ ⎥ ⎦ W( iso ) We have 23 ton basis 23000 kg = 50706.26 Ibm nmix = mmix Mwmix Mwmix = xb * Mwb + x p * Mwp Mwmix = 0.4 * 44.097 + 0.6 * 58.123 = 52.5126 kg / kmol nmix = 23000 = 437.99kmol 52.5126 1 2 W = 11008 .632 × 437.99 = 4821672 .056 kj = 4570130 .246 Btu W = m * ∆H W = m * (H A − H1 ) H1 = xb * H b1 + x p * H p1 At point 1 is superheated region,so we have to use superheated tables for propane and butane. For Butane we have English Units Tables So we need 20 Celcius=68 F & 1bar=14.5038 psi We are making interpolation again. At 60 F & 14.5038 psi our enthalpy is 337.36 Btu/Ibm At 80 F & 14.5038 psi our enthalpy is 345.52 Btu/Ibm 1 3 After final interpolation between 60 F & 80 for 68 F ; Same prodedure for Propane and we have; HB1=340.624 Btu/Ibm HP1=‐656.96 Btu/Ibm H 1 = 0.4 * 340.624 + 0.6 * (−656.96) = −257.9264 Btu / lbm W = m * ( H A − H 1 ) 4570130.246 = 50706.26 × ( H A − (−257.9264)) HA=‐167.79 Btu/Ibm Between the points 2‐B (throttling) T Q ( P = cst ) A B ( H = cst ) Ws 20oC 2 (Saturated Liquid) 1 (Superheated Region) (P = 1 bar) S At point B PB=PA (isobaric cooling) 1 4 At point 2 T2=20 oC= 68 oF P2=5.724 bar (At this point mixture is in saturated vapor + liquid region) H2=HB H [Btu/lbm] Hl [Btu/lbm] v Propane ‐669.47 ‐816.98 n‐Butane 338.32 182.32 Vapor quality xv is too small. So; we can assume it is zero and Hl is used to calculate Hmix at point 2 by saturation tables with their interpolations. l H 2 = xb * H b + x p * H lp H 2 = 0.4 * 182.32 + 0.6 * (−816.98) = −417.26 Btu / lbm H2=HB (throttling process) isenthalpic process. 1 5 Between the points B‐A (cooling) T Q ( P = cst ) A B ( H = cst ) Ws 20oC 2 (Saturated Liquid) 1 (P = 1 bar) (Superheated Region) S Q = n * Cp * ∆T Q = m * (H B − H A ) Q = 437.99 * 84.568 * (TB − 423.324)kJ Q = 50706.26 × (−417.26 + 167.79) = −12649690 .68 Btu = −13345934 .75kJ − 13345934.75 = 437.99 × 84.568 × (TB − 423.324) TB=63.011 K = ‐210 Celcius 1 6 This temperature is not suitable for this process.Reasons of this result are will be explained in discussion part. We need criticalpressure of mixture for calculate the required work between point 1 and point A in this process. The pressure of point A and point B must be greater then critical pressure (PC). Also we assume this mixture is an ideal gas mixture. Because of the process between point 1‐A is an adiabatic and reversible process, this process is isentropic so T P ∆S=0.Then we find T2 using this equation: ∆S = C p In 2 − RIn 2 . Between the same T1 P1 points, the work required for compressor is calculated from the equation: Wiso ⎡ ⎛P = C p T1 ⎢⎜ 2 ⎢⎜ P1 ⎢⎝ ⎣ Cp ⎤ ⎞R ⎟ − 1⎥ . To calculate heat of the process, we also need enthalpy of the ⎟ ⎥ ⎠ ⎥ ⎦ point B. Between point 2‐B is throttling process. As a result of throttling is isenthalpic process, ∆H=0 and H2=HB. At point 2, the quality of vaporization is close to zero, to determine the enthalpy of this point we use specific liquid enthalpies of propane and butane. After all of these calculations, we determine the volume of the 31 ton of LPG. Also we assume the shape of tank is spherical and calculate the radius. 9.2 APPENDIX B The spherical tank incluiding mixture of 40% n‐butane and 60% propane in liquid and vapor phases: 20% VAPOR 80% LIQUID 1 7 Vl[ft3/lbm] Vv[ft3/lbm] m = 23000 kg = 50706.32lbm propane 0.032137 0.879916 n‐butane 0.027754 3.010466 mbu tan e = 0.4 * 23000 = 9200 kg = 20282 .53lbm m propane = 0.6 * 23000 = 13800kg = 30423.79lbm Basis= 100 ft3 20 ft3 vapor (mv lbm) + 80 ft3 liquid (ml lbm) Vapor: mv * xb * Vbv + mv * x p * V pv = 20 ft 3 mv * 0.4 * 3.010466 + mv * 0.6 * 0.879916 = 20 ft 3 Liquid: ml * xb *Vbl + ml * x p *V pl = 80 ft 3 mv = 11.546lbm ml * 0.4 * 0.027754 + ml * 0.6 * 0.032137 = 80 ft 3 Total mass= 2644.53 lbm 1 8 ml = 2632 .982lbm Scale Factor = 50706.32/ 2644.53 = 19.17 • Vapor mass= mv* Scale Factor= 11.546*19.17= 221.38 lbm mpropane = 0.6*221.38= 132.83 lbm Vpropane = mpropane* Vvpropane=116.88 ft3 mbutane = 0.4*221.38 =88.552 lbm Vbutane = mbutane* Vvbutane=266.58 ft3 Vvtotal=383.46 ft3 • Liquid mass= ml* Scale Factor= 2632.982*19.17= 50484.94 lbm mpropane = 0.6*50484.94= 30290.964 lbm Vpropane = mpropane* Vlpropane= 973.46 ft3 mbutane = 0.4*50484.94=20193.98 lbm Vbutane = mbutane* Vlbutane=560.463 ft3 Vltotal=1533.93 ft3 1 9 Total volume=1917.38 ft3 The tank is spherical, so; 4 * Π * R 3 = 1917.38 ft 3 3 R = 7.7 ft = 92.48in Thickness of the tank: t= P*R 2 * S * E − 0.2 * P P = 5.724bar = 83.02 psi S = 16300 psi E = 1 t= 83.02 * 92.48 = 0.2356in = 0.59cm 2 *16300 *1 − 0.2 * 83.02 Corrosion allowance= 0.125in for the material SA‐516 carbon & low alloy steel. Final thickness must be; tfinal = t + corrosion allowance= 0.2356 + 0.125= 0.3606 in = 0.916 cm 2 0 ...
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This note was uploaded on 03/24/2010 for the course CHEMENG che 220 taught by Professor Ferhanatalay during the Spring '09 term at Ege Üniversitesi.

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