Essay: Report: 'SYNTHESIS MANUFACTURING OF AMMONIA'

ABSTRACT
IN THE MANUFACTURING PROCESS OF AMMONIA, VARIOUS STEPS ARE INVOLVED WHERE EACH STEP HAVE DIFFERENT PARAMETER TO FINALIZED THE PRODUCT. NITROGEN AND HYDROGEN ARE REACTED IN PRESENCE OF AIR TO PRODUCED AMMONIA. IN SYNTHESIS PROCESS OF AMMONIA THERE ARE MATERIAL BALANCE AND ENERGY BALANCE ARE REQUIRED FOR UTILIZATION OF ENERGY AND MATERIAL. TO PRODUCE EFFECTIVENESS TOWARDS TO REDUCE COST OF MATERIAL AND ENERGY. THE NATURAL GAS USED AS FEED STOCK FOR AMMONIA PLANT. THE NATURAL GAS CONTAINS CH4, C2H4, CO2, CO, H2 ELEMENTS. FOR SYNTHESIS PROCESS OF AMMONIA, KNOWLEDGE OF CHEMICAL REACTION KINETIC AND THERMAL EQUILIBRIUM DATA ARE REQUIRED WHICH IS NOT IN OPEN LITERATURE.
CHAPTER
1
INTRODUCATION
1.1 PROJECT SUMMARY
The whole process of producing ammonia from methane is summarized . If natural gas from atmosphere is the feedstock, extra processes are needed.natural gas is converted into methane and oxides of carbon before going into the primary reformer and thence to the shift reaction. Coal is also converted into hydrogen and carbon oxides and this mixture then undergoes the shift reaction.
FIG-1(FIG REF-1)
(b) The manufacture of ammonia (The Haber Process)
The heart of the process is the reaction between hydrogen and nitrogen in a fixed bed reactor. The gases, in stoichiometric proportions, are heated and passed under pressure over a catalyst .
FIGURE-2 (FIG REF-2)
The proportion of ammonia in the equilibrium mixture increases with increasing pressure and with falling temperature (Le Chatelier’s Principle). Quantitative data are given in Table 1. To obtain a reasonable yield and favourable rate, high pressures, moderate temperatures and a catalyst are used.
A wide range of conditions are used, depending on the construction of the reactor. Temperatures used vary between 600 and 700 K, and pressures between 100 and 200 atmospheres. Much work is being done to improve the effectiveness of the catalyst so that pressures as low as 50 atmospheres can be used.
As the reaction is exothermic, cool reactants (nitrogen and hydrogen) are added to reduce the temperature of the reactors.
The ammonia is usually stored on site (step 7) and pumped to another part of the plant where it is converted into a fertilizer (urea or an ammonium salt). However it is sometimes transported by sea (Figure 4) or by road, to be used in another plant.
1.2 SCOPE
The validation scope is defined as an independent and objective review of the project design document (PDD). The PDD is reviewed against the criteria stated in Article 12 of the Kyoto Protocol, the CDM modalities and procedures as agreed in the Marrakech Accords and the relevant decisions by the CDM Executive Board, including the approved consolidated baseline and monitoring methodology AM0018, Version 01 /9/. The validation team has, based on the recommendations in the Validation and Verification Manual /11/ employed a risk-based approach, focusing on the identification of significant risks for project implementation and the generation of CERs.
The validation is not meant to provide any consulting towards the project participants. However, stated requests for clarifications and/or corrective actions may have provided input for improvement of the project design.
CHAPTER
2
PHYSICAL PROPERTIES AND CHEMICAL PROPERTIES
Physical Properties of Ammonia
‘ Ammonia is a colorless gas.
‘ It has a pungent odor with and an alkaline or soapy taste. When inhaled suddenly, it brings tears into the eyes.
‘ It is lighter than air and is therefore collected by the downward displacement of air.
‘ It is highly soluble in water: One volume of water dissolves about 1300 volumes of ammonia gas. It is due to its high solubility in water that the gas cannot be collected over water.
‘ It can be easily liquefied at room temperature by applying a pressure of about 8-10 atmosphere.
‘ Liquid ammonia boils at 239.6 K (- 33.5??C) under one atmosphere pressure. It has a high latent heat of vaporization (1370 J per gram) and is therefore used in refrigeration plants of ice making machines.
‘ Liquid ammonia freezes at 195.3 K (-77.8??C) to give a white crystalline solid.
Structure of ammonia
Ammonia is a covalent molecule as is shown by its dot structure. The ammonia molecule is formed due to the overlap of three sp3 hybrid orbitals and orbitals of three hydrogens. The fourth sp3 hybrid orbital is occupied by a lone-pair. This gives a trigonal pyramidal shape to ammonia molecule. The H-N-H bond angle is 107.3??, which is slightly less than the tetrahedral angle of 109??28. This is because the lone pair – bond pair repulsions tend to push the N-H bonds slightly inwards. In liquid and solid states, ammonia is associated through hydrogen bonds.
Chemical Properties of Ammonia
Thermal stability
Ammonia is highly stable. However, it can be decomposed into hydrogen and nitrogen by passing over heated metallic catalysts or when electric discharge is passed through it.
Combustibility
Ammonia is combustible in air. However, it will burn in an atmosphere of oxygen
Nitric oxide is obtained when a mixture of ammonia and air is passed over platinum – rhodium catalyst at 800??C
Basic character
Ammonia molecule has a strong tendency to donate its lone pair of
electrons of nitrogen to other molecules. Thus, it acts like a strong Lewis base. In aqueous solutions, NH3 ionizes in accordance with the reaction.
The equilibrium constant for this reaction at 298 K is 1.8 x 10-5. Thus, ammonia ionizes to a very small extent in aqueous solution. The aqueous solution of ammonia acts as a weak base due to the presence of OH- ions therein. Therefore, ammonia turns red litmus blue and reacts with acids to form salts.
For example,
With metal oxides
Ammonia gets oxidized to nitrogen, when passed over heated metal oxides.
With halogens
Ammonia reacts with halogens but the type of halogen and reaction conditions determine the nature of products.
Chlorine
Nitrogen and ammonium chloride are formed with a limited amount of chlorine. In the presence of excess of chlorine, nitrogen trichloride is formed.
Bromine
It gives ammonium bromide and nitrogen
Iodine
When rubbed with solid iodine, a dark colored precipitate of nitrogen
tri-iodide is obtained
After drying, if NH3.NI3 is struck against a hard surface or hit with a hammer, it explodes producing iodine vapors.
With carbon dioxide (formation of urea)
Ammonia when heated under pressure with CO2 gives urea.
With alkali metals.
CHAPTER
3
LITERATURE REVIEW
AMMONIA PLANT
IFFCO Kalol plant consists of 1100 tpd ammonia plant desiged and engineered by M/s. M.W.Kellogg ,USA.Add on pre-reformer unit is designed by M/s.HTAS, Denmark.
Brief Process Description Of Ammonia Plant:-
For the production of ammonia, hydrogen and nitrogen are required. Hydrogen is obtained by reacting natural gas with steam and nitrogen is obtained from air. Natural gas is supplied by RELIANCE.Natural gas is used as feed stock, whereas associated gas is used as fuel. Natural gas can also be used as fuel by letting down into associated gas header through a letdown station. Process steam is generated within the plant. Natural gas supply is inadequate to meet production capacity, and therefore naphtha based pre-reformer unit has been added.
The manufacture of ammonia involves following operations/ processes :
1. Desulphurisation of natural gas.
2. Pre-reforming & reforming.
3. Water gas shift reaction.
4. CO2 absorption and stripping.
5. Methanation.
6. Refrigeration.
BLOCK DIAGRAM OF AMONIA PRODUCTION
FIGURE-3(FIG REF-3)
Natural gas is supplied by RELIANCE at a pressure of about 40 kg/cm2g. It is then feeding to desulphuriser. The natural gas contains sulphur compounds (3 to 5 ppm max.) which are removed by passing the gas through desulphurisers containing activated carbon. Sulphur free gas is preheated, mixed with steam, again heated and sent to primary reformer.
In primary reformer, the natural gas and steam mixture along with pre-reformed gas from pre-reformer is passed through nickel catalyst, packed in tubes. As the reaction is endothermic, heat is supplied by firing gas and naphtha in primary reformer arch burners. At primary reformer exit, a mixture of hydrogen, carbon monoxide, carbon dioxide and methane is obtained. This mixture is then sent to secondary reformer.
In secondary reformer, the gas mixture is burnt with required quantity of air which is supplied by air compressor. Gas is passed through the secondary reformer which contains chromium and nickel based catalyst to complete the reforming reaction. The gas exit from secondary reformer passes through waste heat boilers to generate high pressure steam which in turn reduces the process gas temperature up to the required high temperature shift reactor.
The gas exit from waste heat boilers is passed through shift converters where carbon monoxide is converted to carbon dioxide. First, gas passes through high temperature shift converter which contains iron catalyst. The exit gas is cooled and then passed through a bed of low temperature shift converter containing zinc-copper catalyst. The gas exit from the low temperature shift converter contains mainly hydrogen, carbon dioxide and nitrogen with small quantity of carbon monoxide.
The synthesis of ammonia demands a high purity of synthesis gas containing only hydrogen and nitrogen in a proportion of 3:1 by volume. The outlet gas from shift converters is sent to CO2 absorber where the gas is brought in contact with a 40% (by weight) aqueous activated methyl di-ethanolamine (a-MDEA) solution for absorption of carbon dioxide from the gas stream. The a-MDEA solution is heated at low pressure in CO2 strippers, where the carbon dioxide is liberated which is cooled down and sent to urea plant.
The gas leaving the absorber contains small amount of carbon monoxide and carbon dioxide. These oxides of carbon are converted to methane as these oxides are poisonous to the ammonia synthesis catalyst. This is achieved in methanator containing highly active nickel catalyst. After the methanation stage, the synthesis gas is cooled down and sent to synthesis gas compressor.
In synthesis compressor, gas is compressed to a high pressure. The recycle gas from the synthesis loop is mixed up with make-up gas in the last stage of the synthesis gas compressor and the combined gas mixture is then sent to the synthesis converter after condensation and separation of ammonia in chillers and separators. In the converter, hydrogen and nitrogen react to form ammonia in presence of iron catalyst.
The outlet gas from ammonia converter is cooled and sent to the last stage of the synthesis gas compressor, thus forming the close loop. Inert gases like argon and methane which are present in small quantities in synthesis gas after methanation, get accumulated in synthesis loop. In order to maintain it within design limits, a small quantity of synthesis gas coming from synthesis converter is purged. Purge gas is sent to purge gas recovery unit to recover hydrogen from the purge gas by a cryogenic process and the hydrogen so recovered is sent to the suction of the synthesis gas compressor.
The separated ammonia is purified by letting down its pressure in steps. A refrigerant compressor is provided to compress the vapour ammonia generated in chillers to cool high pressure synthesis gas for condensation of ammonia and other refrigeration duties in the process. The product ammonia is sent to urea plant at 400 C (known as hot ammonia) and/or to ammonia storage tank at -330 C (known as cold ammonia).
CHAPTER
4
DETAILED DISCRIPTION
For the production of ammonia, hydrogen and nitrogen are required. Hydrogen is obtained by reacting natural gas and naphtha with steam and nitrogen is obtained from air. Natural gas is supplied by GAIL from the near by gas gathering station of ONGC.
Natural gas is used as feed stock, whereas associated gas is used as fuel. Naphtha was used as feed stock, through pre-reformer, as well as fuel. Natural gas can also be used as fuel by letting down into associated gas header through a letdown station. Process steam is generated within the plant. The manufacture of ammonia involves following operations/ processes
1. Desulphurisation of naphtha & natural gas.
2. Pre-reforming & reforming.
3. Water gas shift reaction.
4. CO2 absorption and stripping.
5. Methanation.
6. Ammonia synthesis.
7. Refrigeration
4.1 Natural gas supply and desulphurization :
4.1.1 Natural gas supply and compression:
It is supplied in the range of 8 to 10 kg/cm2g pressure and 200 C to 380 C temperature.
Two turbine driven centrifugal compressors of adequate capacity in series are installed to boost up the pressure of natural gas upto 39 kg/cm2g. Pressure control valves through which natural gas can be vented to atmosphere during start up to control the pressure of the natural gas.
Natural gas at about 10 kg/cm2g enters the natural gas booster compressor suction after passing through suction knock out drum where liquid hydrocarbons if any, are knocked out. Level in is controlled by level control valve. Natural gas booster compressor discharges gas at about 19.5 kg/cm2perature which after passing through after cooler and discharge separator goes to suction knock out drum of natural gas compressor at a temperature of about 400 C.
4.1.2 Natural gas desulphurisation
Natural gas contains sulphur compounds in the form of sulphides, disulphides, mercaptan sulphur, thiophenes etc. which are poisonous to the catalysts used in ammonia plant. The process of removing these sulphur compounds is called desulphurisation. The process employed is adsorption and adsorbent used is activated carbon catalyst. This catalyst adsorbs the sulphur compounds with increasing selectivity in the following order :
(1) Hydrogen sulphide.
(2) Carbonyl sulphide.
(3) Carbon disulphide.
(4) Mercaptan sulphur.
(5) Disulphides.
(6) Thiophenes.
Natural gas enters desulphuriser from top and passes through a bed of activated carbon which adsorbs sulphur compounds. There are two desulphurisers, out of which one is always in line while other one is taken out of line to regenerate the bed and to keep it as standby. The desulphuriser in line normally operates at natural gas line pressure of 39 kg/cm 2g and temperature of 300C to 350 C.
With expected sulphur in natural gas in the order of 0.5-3 ppm (v/v), each bed of activated carbon is expected to exhaust after about 10 months of operation at the design flow rate. However, with sulphur more than anticipated or with catalyst of low activity, bed will be exhausted earlier. This catalyst is expected to last for three to five years depending upon the amount of sulphur in the gas.
4.2 Reforming and waste heat recover:
4.2.1 Primary reforming:
4.2.1.1 Process for Primary reformer:
The natural gas after removal of sulphur compounds in desulphuriser, passes through the tube side of feed preheater to raise the temperature of the gas to 94 0C before entering feed preheat coil in the convection section to avoid fire corrosion of feed preheat coil.
Due to sulphur content in the naphtha fuel, it is necessary to protect feed preheat coil located at the convection section outlet, against corrosion. Condensation of acidic moisture on the outside tube wall of feed preheat coil is to be avoided. Preheating the natural gas by steam prior to the entry to the reformer furnace will maintain the feed preheat coil tube wall temperature above the dew point of the flue gas.The natural gas at 94 0C enters feed preheat coil in the convection section of primary reformer furnace. The natural gas temperature is raised to 270 0C by the flue gas coming out of the convection zone of the furnace.
The reformer feed then passes through the catalyst packed reformer tubes. There are 336 tubes arranged in eight rows of 42 tubes each.
As the reaction is endothermic i.e. it absorbs heat, the heat is supplied by burning mixed fuel gas and naphtha as fuel in 126 top fired arch burners. The catalyst used in the primary reformer is nickel based. Top portion of the tubes is filled with potash based nickel catalyst as safeguard for heavy hydrocarbon from pre-reformer.
For each row of 42 reformer tubes, there is an outlet manifold, located near the floor of primary reformer furnace. There are eight centrally located risers, one on each of the outlet manifolds. These risers lead the gas flow to a water jacketed transfer line also known as effluent chamber located over the top of primary reformer furnace . Temperature of the reformed gas at the outlet of reformer tube is 797 0 C and pressure is 32.7 kg/cm2g. Gas while passing through the risers, picks up more heat from the furnace. Transfer line directs the flow from primary reformer to the inlet of secondary reformer.
4.2.2 Secondary reforming:-
4.2.2.1 Process for secondary reformer:
The partially reformed gas from primary reformer enters the secondary reformer inlet chamber tangentially through transfer line.The temperature of the gas inlet to secondary reformer is around 797 0C. The flow is downward around a centrally located air inlet pipe and passes through a baffle plate and straightening vanes and enter the combustion zone of secondary reformer. Process air supplied by process air compressor is preheated in steam – air preheat coil, located in the convection zone of primary reformer.
The purpose of air preheat coil is :
”to recover heat from flue gas.
”to transfer portion of heat load to secondary reformer from primary reformer.
”to attain higher flame temperature, which favours reforming.
A small quantity of MS steam is mixed at air inlet to air preheat coil in order to ensure continuous positive flow into the secondary reformer in the event of process air failure and to protect the steam air preheat coil from developing excessive temperature during emergencies. Preheated process air at 447 0C temperature and 32.7 kg/cm2g pressure is introduced into the process flow through a John Zink air mixer. This has the effect of better mixing of process gas and complete combustion of the oxygen.
The part of H2 and other combustible gases in the process gas burn with oxygen, leaving the nitrogen required to make ammonia. The amount of air is fixed by the nitrogen requirement for the ammonia synthesis.
4.2.2.2 Reforming reactions in secondary reformer
The reaction with air in secondary reformer (combustion zone) is as follows :
2H2 + O2 + 3.715 N2 ”2H2O + 3.715 N2 + Heat
2CH4 + 3.5 O2 + 13.003 N2 ”CO2 + CO + 4 H2O + 13.003 N2 + Heat
The heat produced by the above exothermic reaction is utilised for completing the remaining methane reforming. The temperature in combustion zone is around 12350 C. The accurate temperature is difficult to predict. The hot gases pass through bed of nickel catalyst. Catalyst used are high temperature resistant chromia and high activity nickel at the top and bottom respectively. The methane steam reforming reaction in secondary reformer is same as that given for primary reformer.
The temperature of the gas exit secondary reformer is 961 C.
4.3 Shift conversion:-
Shift converter is actually a two converter system, high and low temperature. It is constructed with internal dished heads to separate one from the other. The upper converter is the high temperature shift converter and lower one is low temperature shift converter. The process gas flows from secondary reformer via waste heat boilers to high temperature shift converter.
4.3.1 High temperature shift conversion
The reformed gas enters the high temperature section of shift converter at 3450 C to 3700 C temperature and about 31.8 kg/cm2g pressure and flows through the catalyst bed. The bypass around is provided to control high temperature shift converter feed inlet temperature. The catalyst used in high temperature shift converter is copper promoted iron oxide catalyst in reduced state.
The following reaction takes place in shift converter :
CO + H2O ”CO2 + H2
As indicated by this equation, most of the carbon monoxide is converted to carbon dioxide gaining an additional mole of hydrogen per mole of carbon monoxide.
Above reaction is a reversible one, with ‘shifting’ carbon monoxide favoured at lower temperature. However, the rate of reaction is favoured by high temperature
4.3.2 Low temperature shift conversion
The gas coming out of high temperature shift converter still contains about 2.5 % carbon monoxide, which should be reduced to within tolerable limit before sending the gas for CO2 removal and methanation. This is accomplished in low temperature shift converter.
The temperature of inlet gas to low temperature shift converter is about 2000 C when the catalyst is new and 2400C (maximum) when the catalyst is old.Low temperature shift converter contains high copper catalyst .
The shift reaction is same as in high temperature shift converter. The gas comes out of low temperature shift converter at 2150 C (2540 C max.) temperature and 28.2 kg/cm2g pressure.
4.4 Carbon dioxide removal:-
In this section the bulk of CO2 in the raw synthesis gas is removed by absorption, using 40% aqueous activated methyl diethanol amine (a-MDEA) solution, at relatively high pressure and low temperature. The absorption of CO2 involves the reaction of dissolved CO2 in water with a-MDEA to form a loose chemical compound which can be easily dissociated at higher temperature and lower pressure. Following reaction takes place.
CO2 + H2O ”H2CO3
Properties of a-MDEA
Chemical formula : CH3-N(CH2-CH2-OH)2
Molecular weight : 119.16 kg/kgmole
4.4.1 CO2 removal process:
The raw synthesis gas at a pressure of 27.3 kg/cm2g and temperature of 630 C containing about 18 % dry volume of CO2 is introduced at the bottom of CO2 absorber.Absorber is a cylindrical tower fitted with twenty perforated sieve trays one above the other spaced at equal distance. Lean a-MDEA solution from CO2 stripper bottom, is cooled in a-MDEA solution exchanger and then in a-MDEA solution cooler by rich a-MDEA and cooling water respectively. a-MDEA circulation pumps introduces the lean a-MDEA solution over the top tray of the tower at a temperature of 490 C. Solution flows downwards, counter current to the gas flow.
Control of liquid release from bottom outlet is by the pressure drop developed by the liquid head above the gas inlet and all the trays. This operation forces the gas to bubble through liquid and helps to give more contact time. Almost all the CO2 is absorbed by the solution, leaving only small traces (200 ppm) of CO2 in absorber outlet gas. The gas before leaving the tower passes through a demister pad to remove the entrained solution, if any.
4.4.2 a-MDEA regeneration and circulation system
Rich a-MDEA solution from the bottom of absorber is sent to CO2 strippers for regeneration. Strippers operate at a pressure of 0.74 kg/cm2g and temperature of 1180 C at the bottom. Rich a-MDEA solution is heated to 930 C by heat exchange with the lean solution coming from the bottom of strippers, in a-MDEA solution exchangers and then splits into equal stream as feed to CO2 strippers through control valves. These control valves let down the pressure from 27.3 kg/cm2g to 0.74 kg/cm2g. These valves function to control the levels in absorber and strippers.
CO2 stripper towers are fitted with seventeen perforated sieve trays each spaced equally one below the other. The solution enters above the top tray. The function of CO2 strippers is regeneration of rich a-MDEA solution by liberating CO2 absorbed in it, so that the solution can be reused in absorber. The solution in the stripper bottom is heated in reboilers. There are two reboilers for each stripper. Low temperature shifted gas provides major portion of reboiling heat for CO2 strippers in gas reboilers, balance heat is provided by 3.5 kg/cm2g steam in steam reboilers.
The solution from strippers while passing through the tube side of these reboilers, is heated to 1180 C and by thermosyphoning the vapour solution mixture returns to strippers from the top of reboilers. As the vapours rise through the trays, the rich a-MDEA solution together with the reflux pumped from CO2 stripper reflux drum comes in contact with it and condenses the vapours. The CO2 thus stripped off in strippers along with water vapour and a-MDEA vapour leave strippers at a temperature of 890 C. These are cooled by cooling water in CO2 stripper condensers to 540 C. The condensate is separated in CO2 stripper reflux drum.
The lean a-MDEA solution form the bottom of strippers is reused after cooling, for absorption of CO2 in absorber. The lean solution at 1180 C is drawn from the bottom of both strippers, combined in a common header and sent to the shell side of a-MDEA solution exchangers to heat rich a-MDEA solution. The lean solution is further cooled to 490 C in a-MDEA solution coolers with cooling water, before being pumped to absorber by a-MDEA circulation pumps controls flow at the discharge of the pump by varying speed of a-MDEA pump turbine. Thus the a-MDEA circulation systems operates in a closed circuit.
4.5 Methanation:-
For ammonia synthesis a very pure gas mixture of H2 and N2 in the ratio of 3:1 (by volume) is required and the small amounts of CO2 and CO as seen in the above analysis are poisonous to the ammonia synthesis catalyst.
These oxides are removed by converting them into methane in methanator by a highly active nickel based catalyst in presence of H2.
This step is known as methanation. Methane has no action on the ammonia synthesis catalyst, but it accumulates in the synthesis loop as inert.
Methanation reactions are given below :
CO + 3H2 ”CH4 + H2O
CO2 + 4H2 ”CH4 + 2H2O
Both these reactions are highly exothermic, and hence extreme care is to be observed while operating methanator. The unit is properly protected with high temperature alarms and shut off systems. Methanator vessel, filled with nickel catalyst, operates at inlet temperature of around 3000 C- 3150 C.
As methanation reaction takes place at elevated temperature, the absorber effluent gas is heated to the reaction temperature in two heat exchangers, the first being synthesis gas- methanator feed exchanger where the gas while flowing through the shell side gains temperature up to 1160 C.
In the second exchanger, methanator feed heater gas is heated up further to 3000 C – 3150 C. A part of the gas bypassing the exchanger, controlled by is for proper temperature control. The exchanger outlet joins the bypassed gas and the combined stream enters the top of methanator.
4.6 Ammonia synthesis:-
4.6.1 Synthesis gas compression:-
The pure synthesis gas mixes with the recovered hydrogen from the purge gas recovery plant. The mixture is then compressed in a turbine driven two case centrifugal compressor. Inter case cooling and chilling is provided for optimum volumetric efficiency and also to condense out water of saturation and hence the reduces the power requirements of the machine. Recycle gas mixture consisting of ammonia (14.75 % by volume) and unreacted reactants from synthesis converter is admitted in the last wheel of the second case and mixes with synthesis gas mixture (make up gas as it is called) and undergoes final stages of compression to approximately 137 kg/cm2g and temperature of 65.30 C. The compressor discharge gases are then cooled to 400 C with cooling water in synthesis gas compressor after cooler
4.6.2 Synthesis loop
The make up gas and recycle gas mixture with the conditions mentioned above flows into ammonia synthesis loop through a motor operated block valve.The gas is cooled successively in three chillers using liquid ammonia as refrigerant operating at successively lower temperatures to condense the ammonia contained in the gas before it is sent to ammonia converter for synthesis. The gas from splits into two parallel streams.The major flow passes through the tube side of chillers in succession and is cooled to 210 C in first chiller and then to 20 C in second chiller. The minor stream flows to shell side of converter feed/feed & recycle gas exchanger where it exchanges heat with the cold stream of ammonia separator outlet gases. The gas cools down to 0.010 . A hand control valve control the flow through this exchanger. The gas stream then combine together and enters the tube side of feed and recycle gas third stage chiller. Here the gas is cooled to -230 C.
Gas flow now enters ammonia separator.All the condensed ammonia in the gas is separated here. Valve controls the level in this separator. The ammonia separated forms main part of product ammonia. Alongwith liquid ammonia, the water vapours contained in synthesis gas together with small traces of carbon dioxide and left out carbon monoxide after methanation are also removed in this separator. This serves as another purification step for the gas before entering the converter catalyst bed.Converter feed leaving ammonia separator enters the tube side of converter feed/ feed recycle gas exchanger and gains heat from a part of the incoming feed. outlet gas temperature is around 210 C. Now the gas flows to converter feed / effluent exchanger where temperature is raised to 1350 C.
Ammonia synthesis reaction is not a once-through process. So the H2 : N2 mixture contained in the gas is again recycled back to converter after removing product ammonia and making up the pressure. Converter effluent gases from converter interchanger exchanges heat with boiler feed water from deaerator and gets cooled to 1600 C in ammonia converter boiler feed water heater. It then flows to ammonia converter feed/effluent exchanger and exchanges heat with the incoming feed and gets cooled to 430 C. The gas called ‘recycle gas’ goes to the last wheel of second case of synthesis gas compressor. The whole process as mentioned above, from synthesis gas compressor discharge to the suction of the recycle gas stage is a closed circuit system and is termed as the ‘Ammonia Synthesis Loop’.
CHAPTER
5
MATERIAL BALANCE
5.1 Desulphuriser:
Inlet composition of Natural gas: (Table 4.1)
Basis: 894.93 kmol/hr NG flow
Component Vol% Mol%(kmol) Molar mass Kg mass Mass%
CH4 97.81 97.81 16 1564.96 95.89%
CO2 0.35 0.35 44 15.4 0.94%
N2 1.84 1.84 28 51.52 3.15%
S 3 ppm 3 ppm 32
Total 1631.88 99.99=100%
Outlet NG Composition is same as inlet but concentration of S in outlet is in the range of 0.1ppm to 0.2ppm. (Table 4.2)
Component Vol% Mol%(kmol) Molar mass Kg mass Mass%
CH4 97.81 97.81 16 1564.96 95.89%
CO2 0.35 0.35 44 15.4 0.94%
N2 1.84 1.84 28 51.52 3.15%
S 0.1-0.2 ppm 0.1-0.2 ppm 32
Total 1631.88 99.99=100%
5.2 Primary Reformer:
Inlet composition (Table 4.3)
Basis: 894.93 kmol/hr
Component Vol% Mol%(kmol) Molar mass Kg mass Mass%
CH4 97.81 97.81 16 1564.96 95.89%
CO2 0.35 0.35 44 15.4 0.94%
N2 1.84 1.84 28 51.52 3.15%
S 0.1-0.2 ppm 0.1-0.2 ppm 32
Total 1631.88 99.99=100%
Outlet composition from primary reformer: (Table 4.4)
Component Mole% Kmol/hr Molar mass Kg mass Mass%
H2 65.49 586.08 2 1172.16 11.41
N2 0.64 7.42 28 207.76 2.02
CO 8.66 77.50 28 2170 21.13
CO2 12.51 111.95 44 4925.8 47.98
CH4 12.50 111.86 16 1789.76 17.43
Ar 61 ppm 61 ppm
Total 10265.48 99.97=100
H20 2625.69
5.3 Secondary Reformer
Inlet composition to secondary reformer from primary reformer: (Table 4.5)
Component Mole% Kmol/hr Molar mass Kg mass Mass%
H2 65.49 586.08 2 1172.16 11.41
N2 0.64 7.42 28 207.76 2.02
CO 8.66 77.50 28 2170 21.13
CO2 12.51 111.95 44 4925.8 47.98
CH4 12.50 111.86 16 1789.76 17.43
Ar 61 ppm 61 ppm
Total 10265.48 99.97=100
Therefore, outlet gas composition from secondary reformer: (Table 4.6)
Component Kmol/hr Mol% Molar mass Kg mass Mass%
CH4 – –
CO 161.395 11.52 28 4519.06 21.30
CO2 139.915 9.99 44 6156.26 29.028
H2 780.554 55.74 2 1561.108 7.36
N2 313.98 22.42 28 8791.44 41.45
Ar 4.51 0.322 40 180.4 0.8492
Total 1400.354 21208.268 99.98=100
H2O 2654.936
4.4 Shift Converter:
Reaction in shift converter:
CO+H2O=CO2+H2
Here, we are taking 100% conversion of CO into CO2 .
Inlet gas composition to shift converter unit: (Table 4.7)
Component Kmol/hr Mol% Molar mass Kg mass Mass%
CH4 – –
CO 161.395 11.52 28 4519.06 21.30
CO2 139.915 9.99 44 6156.26 29.028
H2 780.554 55.74 2 1561.108 7.36
N2 313.98 22.42 28 8791.44 41.45
Ar 4.51 0.322 40 180.4 0.8492
Total 1400.354 21208.268 99.98=100
H2O 2654.936
Outlet gas composition from shift converter unit: (Table 4.8)
Component Kmol/hr Mol% Molar mass Kg mass Mass%
CH4 –
CO –
CO2 301.37 19.29 44 13260.28 54.99
H2 941.949 60.31 2 1883.898 7.81
N2 313.98 20.10 28 8791.44 36.46
Ar 4.51 0.28 40 180.4 0.74
Total 1516.72 24116.018 100
H2O 2493.541
5.5 CO2 absorber:
Inlet composition to CO2absorber: (Table 4.9)
Component Kmol/hr Mol% Kg/hr Mass%
CH4 _ _ _ _
CO _ _ _ _
CO2 301.31 19.29 13257.64 70.61
H2 941.949 60.31 941.949 5.016
N2 313.98 20.10 4395.72 23.41
Ar 4.51 0.38 180.04 0.95
Total 1561.749 100.00 18775.349
Outlet composition of gas mixture:- (Table:4.10)
Component Kmol/hr Mol% Kg/hr Mass%
CH4 _ _ _ _
CO _ _ _ _
CO2 _ _ _ _
H2 941.949 74.73 1883.898 17.35
N2 313.98 24.91 8791.44 80.98
Ar 4.51 0.3578 180.40 1.66
Total 1260.439 100.00 10855.73
H2O negligible
5.6 Methanator:
Inlet composition of gas mixture:- (Table:4.10)
Component Kmol/hr Mol% Kg/hr Mass%
CH4 _ _ _ _
CO _ _ _ _
CO2 _ _ _ _
H2 941.949 74.73 1883.898 17.35
N2 313.98 24.91 8791.44 80.98
Ar 4.51 0.3578 180.40 1.66
Total 1260.439 100.00 10855.73
Outlet composition from methanator will be:- (Table 4.11)
Component Kmol/hr Mol% Kg/hr Mass%
CH4 0.011 0.0008 1.6 0.002
CO _ _ _ _
CO2 _ _ _ _
H2 941.949 74.73 941.949 17.06
N2 313.98 24.91 4395.72 79.65
Ar 4.51 0.3578 180.40 3.26
Total 1260.439 5518.69
H2O negligible
5.7 ammonia synthesis:
inlet composition to ammonia synthesis will be:- (Table 4.11)
Component Kmol/hr Mol% Kg/hr Mass%
CH4 0.011 0.0008 1.6 0.002
CO _ _ _ _
CO2 _ _ _ _
H2 941.949 74.73 941.949 17.06
N2 313.98 24.91 4395.72 79.65
Ar 4.51 0.3578 180.40 3.26
Total 1260.439 5518.69
H2O negligible
outlet composition of ammonia synthesis :
Component Kmol Mole Kg/hr Mass
hr % %
H2 209.835 53.53 419.67 3.49
N2 69.945 17.84 1958.46 32.61
CH4 + Ar 43.85 11.19 2455.6 40.89
CO – – – –
CO2 – – – –
NH3 68.91 17.43 1171.47 19.50
S – – – –
H2O
purge stream data:
Component
Kmol Mole Kg/hr Mass
Hr % %
H2 209.835 60.37 419.67 8.00
N2 69.945 20.12 1958.46 37.37
CH4 + Ar 43.85 12.62 2455.6 46.86
CO – – – –
CO2 – – – –
NH3 23.91 6.87 406.47 7.75
S – – – –
H2O
Recycle stream:
17
Component Kmol Mole Kg/hr Mass
Hr % %
H2 205.05 60.67 410.01 8.05
N2 68.35 20.22 1913.8 37.58
CH4 + Ar 42.85 12.68 2399.6 47.12
CO – – – –
CO2 – – – –
NH3 21.69 6.42 368.73 7.24
S – – – –
H2O
CHAPTER
6
ENERGY BALANCE
Basis: 30000 Kg/hr of NG flow
Avg. Mol Wt = 21.22 Kg/Kmol
Component Mole%
CH4 83.63
C2H6 7.17
C3H8 2.86
C4H10 0.79
C5H12 0.16
CO2 5.21
N2 0.11
O2 0.1
Values of a, b, c and d
Component A b x 103 c x 106 d x 109
CH4 19.2494 52.1135 11.973 -11.373
C2H6 5.4129 178.0872 -67.3749 8.7147
C3H8 -4.227 306.264 -158.6315 32.1465
C4H10 -8.833 419.5341 233.6331 51.0434
C5H12 -3.6266 487.4859 -258.0312 53.0488
CO2 21.3655 -64.2841 -41.0506 -9.7999
N2 29.5905 -5.141 13.1829 -4.968
O2 26.0257 11.7551 -2.3426 -0.5628
Enthalpy Values
Component 25??C 525??C 785??C 797??C 817??C 961??C
Kcal/Kg Kcal/Kg Kcal/Kg Kcal/Kg Kcal/Kg Kcal/Kg
CO2 -94051 -88621 -85303 -85145 -84881 -82951
H2 0 3501 5365 5452 5898 6658
H2O -57797 -53404 -50982 -50862 -50660 -49180
N2 0 3582 5585 5686 5839 6996
CH4 -17888 -11995 -7718 -7505 -7146 -4466
C2H6 -20235 -10383 -3081 -2718 -2109 2427
C3H8 -24819 -10383 -189 327 1195 7642
C4H10 -29811 -11212 2330 2999 420 12451
C5H12 -34999 -12175 4496 5319 6699 16943
CO -26415 -22802 -20770 -20674 -20513 -19341
NH3 -11039 -5847 -2461 -2295 -2016 48
amix = 16.65793427
bmix = 82.89877413 x 10-3
cmix = 2.1220704 x 10-6
dmix = -4.96671026 x 10-9
6.1) Around Heat Exchanger :
Steam is the heating medium.
Total NG flow = 30000 Kg/hr
= 1413.76 Kmol/hr T1 = inlet temperature = 85’C = 358’K T2 = outlet temperature = 94’C = 367’K
HEAT LOAD :-
H = mCpmixdt
= m[a + bT + CT2 + dT3] dt
= m [a(t2-t1) + b (t22-t12) + c(t23-t13) + d(t24-t14)]
= 1413.76 [16.658(367-358) + 82.899×10-3 (3672-3582)
+ -2.122 x 10- 6 (3673-3583) + -4.967 x 10-9 (3674-3584)
= 1413.76 [149.922 + 270.4579875 ‘ 2.509725474 ‘ 2.129745067]
= 587770.72 KJ/hr.
6.2) Around feed preheater coil:
Hot flue gases is the beating medium
T1 = inlet temperature = 94’C = 367’K
T2 = outlet temperature = 270’C = 543’K
HEAT LOAD :-
H = m ??T2mCpdt
T1
= 1413.76 [16.658(543-367) + 82.899×10-3 (5432-3672)
2
+ -2.122 x 10-6 (5433-3673) +-4.967×10-9 (5434-3674)
3 4
= 1413.76 [2931.808 + 6236.781917 ‘ 78.28209652 ‘ 85.42595045]
= 12730739.15 KJ/hr
.
6.3) Heat Load for Primary Reformer :
T1 = inlet temp. = 525’C = 798’K
T2 = outlet temp = 817’C = 1090’K
TABLE: 6.4
Component Inlet Enthalpy Enthalpy
(Kmol/hr) At 525?C (molar)
(Kcal/kgmol)
CH4 2069.55 -11995 -749.68
C2H6 101.22 -10383 -361.1
C3H8 43.81 -10644 -241.9
C4H10 6.01 -11212 -193.31
C5H12 1.52 -12175 -169.09
CO2 61.95 -88621 -2014.11
N2 0.15 3582 127.92
O2 — -22802 -814.35
H2 — 3501 1750.5
H2O 6916.67 -53404 -2966.8
TABLE: 6.5
Component Inlet Enthalpy Enthalpy
(Kmol/hr) At 525?C (molar)
(Kcal/kgmol)
CO2 61.95 -84881 -1929.11
CO 2190.36 -205.13 -732.6
H2 6332.19 5598 2799
Enthalpy of Reaction = (Enthalpy of Products) ‘ (Enthalpy of Reactants)
= {(61.95) (-84881) + (2190.36) (-205.13) + (6332.19) (5598)}
{(2069.55) (-11995) + (101.22) (-10383) + (43.81) ( -10644)
+ (6.01) (-11212) + (1.52) (-12175) + (61.95) (-88621)
+ (0.15) (3582) + (6916.67) (-53404)}
= 29739913.12 + 401294801.60
= 431034714.7 Kcal/hr.
6.4) Heat Load in Riser Tube :-
The process gas gets heated up while rising in the riser tube
T1 = Inlet temp. = 785’C = 1058 ??K
T2 = Outlet temp. = 817’C = 1090 ??K
Cp Value for CH4 :
Cp1058K = a + bT + cT2 + dT3
= 19.2494 + 52.1135 x 10-3 x 1058 + 11.973 x 10-6 x 1058
+ (-11.3173 x 10-9 x 1058)
= 74.39813846 KJ/Kmol K
= 17.774 Kcal/Kmol K
Cp1090K = a + bT + cT2 + dT3
= 19.2494 + 52.1135 x 10-3 x 1090 + 11.973 x 10-6 x 1058
+ (-11.3173 x 10-9 x 1090)
= 76.06615323 KJ/Kmol K
= 18.172 Kcal/Kmol K
Cp Value for CO2 :
Cp1058K = a + bT + cT2 + dT3
= 21.3655 + (64.2841 + 10-3 x 1058) ‘ (41.0506 x 10-6 x 10582)
+ (9.7999 x 10-9 x 10583))
= 55.033 KJ/Kmol K
= 13.148 Kcal/Kmol K
Cp1090K = 21.3655 + (64.2841 + 10-3 x 1090) ‘ (41.0506 x 10-6 x 10902)
+ (9.7999 x 10-9 x 10903))
= 55.354 KJ/Kmol K
= 13.224 Kcal/Kmol K
Cp Value for N2 :
Cp1058K = a + bT + cT2 + dT3
= 29.5905 + (-5.141 x 10-3) x 1058 + (13.1829 x 10-6) (10582)
+ (4.968 x 10-9) (10583)
= 33.024 KJ/Kmol K
= 7.889 Kcal/Kmol K
Cp1090K = 29.5905 + (-5.141 x 10-3) (1090) + (13.1829 x 10-6 x 10902)
+ (4.968 x 10-9) x (10903)
= 33.216 KJ/Kmol K
= 7.935 Kcal/Kmol K
Cp Value for CO :
Cp1058K = a + bT + cT2 + dT3
= 29.0277 ‘ (2.1865 x 10-3 x 1058) + (11.6437 x 10-6 x 10582)
+ (4.7065 x 10-9 x 10583)
= 34.174 KJ/Kmol K
= 8.1643 Kcal/Kmol K
Cp1090K = a + bT + cT2 + dT3
= 29.0277 ‘ (2.1865 x 10-3 x 1090) + (11.6437 x 10-6 x 10902)
+ (4.7065 x 10-9 x 10903)
= 34.383 KJ/Kmol K
= 8.214 Kcal/Kmol K
Cp Value for H2 :
Cp1058K = a + bT + cT2 + dT3
= 28.6105 + (1.0194 x 10-3 x 1058) + (-01476 x 10-6 x 10582)
+ (0.769 x 10-9 x 10583)
= 30.4345 KJ/Kmol K
= 7.271 Kcal/Kmol K
Cp1090K = a + bT + cT2 + dT3
= 28.6105 + (1.0194 x 10-3 x 1090) + (-01476 x 10-6 x 10902)
= (0.769 x 10-9 x 10903) 30.5422 KJ/Kmol K
= 7.296 Kcal/Kmol K
Cp Value for H2O :
Cp1058K = a + bT + cT2 + dT3
= 32.4921 + (0.0796 x 10-3 x 1058) + (13.2107 x 10-6 x 10582)
+ (-4.5474 x 10-9 x 10583)
= 41.9785 KJ/Kmol K
= 10.029 Kcal/Kmol K
Cp1090K = a + bT + cT2 + dT3
= 32.4921 + (0.0796 x 10-3 x 1090) + (13.2107 x 10-6 x 10902)
+ (-4.5474 x 10-9 x 10903)
= 42.3855 KJ/Kmol K
= 10.126 Kcal/Kmol K
TABLE: 6.6
Cp Values
Component Cp 1058 Cp1090 Cpmolal
CH4 17.77 18.17 1.11
CH2 13.15 13.22 0.299
N2 7.89 7.94 0.283
CO 8.16 8.21 0.291
H2 7.27 7.30 3.64
H2O 10.03 10.13 0.557
Since, the Cp Values at the inlet and outlet are mostly the same, taking Cp values at the inlet only
Cpmixture dry:
= (0.125 (17.77) + (0.1251) (13.15) + (0.0083) (7.89) + (0.08706) (7.89) + (0.0806) (8.16) + (0.6549) (7.27) + (0.6549) (7.27)
= 9.350621 Kcal/Kmol K
Heat load For Dry Gas :
Hd = 9.351 (1090 ‘ 1058) x 1979.26 = 592257.3779 Kcal/hr
Heat load for H2O :
H H20 = 10.03 (1090 ‘ 1058) x 6916.67 = 2219973.33 Kcal/hr
Total Heat load = Hd + H H20
= 592257.3779 + 2219973.33
= 2812230.708 Kcal/hr.
‘ Total Head load in the Primary Reformer :
= 431034714.70 + 2812230.708
= 433846945.4 Kcal/hr
6.5) Heat load in Secondary Reformer :
T1 = Inlet temp. = 797’C = 1070 ??K
T2 = Outlet temp = 961’C = 1234 ??K
TABLE: 6.7
Inlet and outlet values
Component Inlet Kmol/hr Enthalpy Outlet Enthalpy
797’C (Kmol/hr) 961’C
Kcal/Kgmol Kcal/Kgmol
N2 0.15 5686 1761.51 6996
CO 2190.36 -206.74 2380.00 -19341
CH4 276.80 -7505 0.831 -4466
CO2 61.95 -85145 116.88 -82951
H2 6332.19 5452 6427.05 6658
H2O 4726.29 -50862 5183.36 -49180
Air introduced to the Secondary Reformer is 2229.57 Kmol/hr
REACTION:
CO + H20 ===> CO2 + H2
‘ OxygenContent
‘ =468.209(21%) Kmol/hr
‘ NitrogenContent =1761.36(79%) Kmol/hr
Absolute Enthalpy at this temperature,
for N2 = 5130Kcal/Kgmol
for O2 = 5250 Kcal/Kgmol
Heat of Reaction (Hr)
= (Absolute Enthalpies of Product) ‘ (Absolute
Enthalpy of Reactants)
={(1761.51)(6996) + (2380)(-19341) + (0.831) (-4466) + (116.88)(-82951) + (6427.05) (6658) + (5183.36) (-49180)} ‘ {(0.15) (5686) + (2190.36) (-20674) + (276.8) (-7505)+ (61.95) (-85145) + (6332.19) (5452) + (4726.29) (-50862)}
=-255533426.1 ‘ (-258500228.6)
=2966802.5 Kcal/hr.
Flow rate of outlet gas:4659.997 kgmol/hr
So, enthalpy of outlet gas=2966802.5 *4659.997/100 = 1.82268*106 KJ/hr
6.6) Shift converter :
1) Around High temp. S.C. : Inlet temp = 365’C
Outlet temp = 422’C
Taking reference temp, as 25??C Enthalpy of reactants
= 14508.75 [28.1337(365-25) + 1972*10-3 (3652-252)
+ 0.909*10-6(3653-253) ‘ 0.528*10-9 (3652-252)
=143745266.5 Kcal/hr
Now for outlet flow rate,
amix = 27.491 bmix = 10.574*10-3
cmix = -3.905*10-6 dmix = .8878*10-9
For reaction at 25??C
Hp = 14508.75 [27.491 (422-25) + 10.574*10-3 (4222-252)
+ 3.905*10-6(3653-253) ‘ 0.8878*10-9 (4224-254)
3
= 170643064.3 Kcal/hr
Co (g) + H2O (g) = CO2(g) + H2(g)
Heat of reaction at 25??C
Heat of Reaction (Hr) = (Heat of formation of Product) ‘ (Heat of formation of reactants)
= (-94081 + 0) ‘ (-26415 ‘ 57797)
= -9839 Kcal/Kmol
Total heat of reaction = 9839 (249.145 ‘ 1142.25)
= -8787260.095 Kcal/hr
Desired heat of reaction,
Hr = 40755448.8 ‘ 8787260.095 ‘ 143745266.5 = -111777077.7 Kcal/hr
By heat balance, heat required to remove by indirect heat exchanges= enthalpy of gas in +heat of reaction ‘ enthalpy of gas receiving
=14374526.6 + 14207493 ‘ 34569897
= 72.084049*106 KJ/hr
6.7)around methanator:
Reaction (1) CO2 + 4H2 = CH4 + 2H2O + Heat
(2) CO + 3H2 = CH4 + H2O + Heat
Inlet temp = 315 C = 588 K
Outlet temp = 360 C = 633 33K
amix = 7.9495 bmix = .9933*10-3
cmix = 3.46*10-6 dmix = -1.3792*10-9
H = -m[a + bT + cT2 + dT3] dt
= 8266.08 [7.9495 (588-298) – .9933*10-3 (5882-2982) + 3.46*10-6 (5883-2983) 1.3792*10-9 ‘ (5884-2984)
= 4625180.618 Kcal/hr
Now for outlet flow rate,
amix = 28.7416 bmix = .3944*10-3
cmix = 3.178*10-6 dmix = -.796*10-9
Hp = 9630 [28.741 (633-298) – 0.3944*10-3 (6332-2982) 2
+ 3.178*10-6 (6333-2983) – 0796*10-9 (6334-2984)]
= 21860561.98 Kcal/hr
Heat of Reaction on No.1 (Hr)
= (Heat of formation of Product)-(Heat of formation of reactants)
= (-17888 + 2(-57797)) ‘ ((-94051+410))
= -39431 Kcal/Kmol
Moles of CO2 at inlet flow rate of .01 kmol/hr
Hr 1 = -39431 * .41
= -19321.19 Kcal/hr
Heat of Reaction on No.2 (Hr)
= (Heat of formation of Product) ‘(Heat of formation of reactants)
= (-17888 + (-57797)) ‘ (-26415)
= -49270 Kcal/kmol
Moles of CO at inlet flow rate of 7.33 kmol/hr Hr2
= -49270 * 7.33
= -361149.1 Kcal/hr
Hr = Hr1 + Hr2
= -19321.19 ‘ 361149.1
= -380470.29 Kcal/hr
By energy balance, loss= heat with in + heat f reaction ‘ heat with out
= 25.441471*106 + 380470.29 *106 ‘ 60.51862 * 10 6
= 3.4696678*106
Flow outlet of outlet stream=2768.393 kmol/hr Q={21860561/100}* 2768.393
= 60.51862 * 10 6 kmol/hr
6.8) Around Ammonia Convertor:
Inlet temp = 135 C = 408 K
Outlet temp = 320 C = 593 K
amix = 27.294 bmix = 3.1164*10-3
cmix = 3.664*10-6 dmix = -1.265*10-9
H = -m[a + bT + cT2 + dT3] dt
= 70814.73 [27.294 (408-298) + 3.1164*10-3 (4082-2982)
+ 3.664*10-6 (4083-2983) ‘ 1.265*10-9 (4084-2984)
= 53590516.24 Kcal/hr
amix = 145.66 bmix = 7.891*10-3
cmix = 4.636*10-6 dmix = -1.6705*10-9
HP= 62757.96 [145.66 (593-298) + 7.891*10-3 (5932-2982)
+ 4.636*10-6 (5933-2983) ‘ 1.6705*10-9 (5934-2984)]
= 275477364.8 Kcal/hr
Reaction : N2 + 3H2 = 2NH3 + Heat
Heat of this reaction at 25??C Hr
= 2(-11039)
= -22078 Kcal/kmol
Total Heat of reaction = -22708(9432.52 ‘ 1430.45) = -166371485.7 Kcal/hr
This heat is taken on by the input stream to attain the temp. of 135??C. By energy balance,
loss= heat input + heat of reaction ‘ heat out
= 1.501479*108 + 65.63 * 106 – 1.52577468*108
=63.201321*106 kj/hr
ENERGY BALANCE DATASHEET:
CHAPTER
7
DESIGN OF ADSORBER
For diameter :
The flow chart for steps of calculating the diameter is shown below:
CALCULATION;
Assume specific velocity is 100 feet / min
?? mi yi , pressure 20 bar , t = 250 c
Total flow rate = 4833.73 kg/hr
Total mol flow rate = 323.63 kmol/ hr
And ??mi yi = 8.72
Q=P * ?? mi yi /R T
Q = 20*8.73/0.08250*250 m3 / hr
= 8.66 m3/hr
vol. flow rate = 4833.73 / 6.903
= 700.23 m3/hr
height = NTU * HTU
assume NTU = 15 , HTU = 0.6
height = 9 m
Area = vm / specific velocity = 0.3828 m2
Now di = 0.7 m , height = 9 m
”internal design pressure = (20 bar ‘ 1 atm) * 1.1
th = p ri / f j ‘ 0.6p + C.A
MOC of material is M.S , SA516 GRADE 70
allowable stress f = 6 * 107 pa = 600.16698 = 600 bar
j= 0.85
C.A =1.5
By internal design pressure p = 21.9
”For shell
= P ri / fj ‘ 0.6 p + C.A
= 21.9 *0.35 /(600 * 0.85) ‘(0.6 * 21.9) +0.015
= 0.03042 m = 30 mm
Weight of shell = ??/4 (D02 ‘ Di2) * L *??
D0 = 0.76 m
Weight = 5000 kg (approx.)
”For top head
th = p Di v / 2fj ‘ 0.2 p + C.A
= 21.9 * 0.7 * 1 / (2*600*0.45)-(0.2*21.9) + 0.015
= 30 mm
th = 30 * 1.06 = 31.8 mm
now weight of top head = ??/4 * (B.D)2 * th * ??
dia = 0.7m = 70 cm = 28 inch
B.D = 36 inch = 91.44 mm = 0.91 m
Weight of top head = 650 kg
So total weight of top and bottom head = 2* 650 = 1300 kg
”total weight = 5000+1300 = 6300 kg
CHAPTER
8
PLANT LOCATION AND LAYOUT
8.1) Plant Layout:
After the process flow diagrams are completed and before detailed piping, structural, and electrical design can begin, the layout of the process units in a plant and equipment within these process units must be planned. This layout can play an important part in determining construction and manufacturing costs, and thus must be planned carefully with attention being given to future problems that may arise. Since each plant differs in many ways and no two plant sites are exactly alike, there is no one ideal plant layout. However, proper layout in each case will include arrangement of processing areas, storage areas, and handling areas in efficient coordination and with regard to such factors as:
”New site development or addition to previously developed site
”Type and quantity of products to be produced
”Possible future expansion
”Operational convenience and accessibility
”Type of process and product control
”Economic distribution of utilities and services
”Type of process and product control
”Economic distribution of utilities and services
”Health and safety considerations
”Waste-disposal problems
”Auxiliary equipment
”Space available and space required
”Roads and railroads
Preparation of the layout: Scale drawings, complete with elevation indications, can be used for determining the best location for equipment and facilities. Elementary layouts are developed first. These show the fundamental relationships between storage space and operating equipment. The next step requires consideration of the operational sequence and gives a primary layout based on flow of materials, unit operations, storage, and future expansion. Finally, by analyzing all the factors that are involved in plant layout, a detailed recommendation can be presented, and drawings and elevations, including isometric drawings of the piping systems, can be prepared. Three-dimensional models are often made.
8.2) PLANT LOCATION
Plant location is however one of the most important part of final planning. Selection of suitable location of the plant is very important because success of the plant is based on this point.
The geographical location of the final plant can have a strong influence on the success of an industrial venture. Much care must be exercised in choosing the plant site, and many different factors must be considered. Primarily, the plant should be located where the minimum cost of production and distribution can be obtained, but other factors, such as room for expansion and general living conditions, are also important.
An approximate idea as to the plant location should be obtained before a design project reaches the detailed-estimate stage, and a firm location should be established upon completion of the detailed-estimate design. The choice of the final site should first be based on a complete survey of the advantages and disadvantages of various geographical area and, ultimately, on the advantages and disadvantages of available real estate. The following factors should be considered in choosing a plant site:
”Raw materials
”Markets
”Power and fuel
”Climate Sinario
”Transportation facilities
”Water supply
”Waste disposal
”Labor supply
”Taxation and legal restrictions
”Site characteristics
”Flood and fire protection
”Community factors
CHAPTER
9
SAFETY AND ENVIRONMENT
9.1) PRINCIPLE OF PROTECTION & PREVENTION:
Industrial accidents are caused by negligence of employer, the worker or the both. Employers’ efforts to reduce the accidents are generally motivated by four considerations.
‘ To lessen human suffering
‘ To prevent damage to plant and machinery
‘ To reduce the amount of time lost as a result
‘ To hold the expenses of workman’s compensation to a minimum.
The basic reasons for preventing industrial accidents are human and economic. The most important of these should be to avoid human suffering. Pain, suffering and wrecked lives are not to be the byproducts of any industry.
FIRE FIGHTING APPLIANCES :
Type of Class A Class B Class C
extinguisher
Carbon dioxide Suitable for surface Suitable. Does not Suitable. Non-
fires only leave residue or conductor and
affect equipment or does not damage
food stuff. equipment.
Dry chemical Suitable for small Suitable. Chemical Suitable.
fire releases smothering Chemical is non-
gas and shields conductor or dry
operator from heat. chemical shields
operator from
heat.
Foam Suitable. Has both Suitable. Unsuitable. Foam
smothering effect Smothering blanket being a conductor
and wetting action. does not dissipate, Should not be
floats on top of Used on live
spilled liquid. equipment.
Water Suitable. Water Unsuitable. Water Unsuitable. Water
saturates material a will spread and not being conductor
9.2) SAFETY CONSIDARATION:
EYE EFFECTS:
Mild concentrations of product will cause conjunctivitis. Contact with higher concentrations of product will cause swelling of the eyes and lesions with a possible loss of vision.
SKIN EFFECTS:
Mild concentrations of product will cause dermatitis or conjunctivitis. Contact with higher concentrations of product will cause caustic-like dermal burns and inflammation. Toxic level exposure may cause skin lesions resulting in early necrosis and scarring.
INGESTION EFFECTS:
Since product is a gas at room temperature, ingestion is unlikely.
INHALATION EFFECTS:
Corrosive and irritating to the upper respiratory system and all mucous type tissue. Depending on the concentration inhaled, it may cause burning sensations, coughing, wheezing, shortness of breath, headache, nausea, with eventual collapse. Inhalation of excessive amounts affects the upper airway (larynx and bronchi) by causing caustic-like burning resulting in edema and chemical pneumonitis. If it enters the deep lung, pulmonary edema will result.
9.3) FIRST AID MEASURES:-
EYES:
Flush contaminated eye(s) with copious quantities of water. Part eyelids to assure complete flushing. Continue for a minimum of 15 minutes. persons with potential exposure to ammonia should not wear contact lenses.
SKIN:
Remove contaminated clothing as rapidly as possible. Flush affected area with copious quantities of water. In cases of frostbite or cryogenic “burns” flush area with lukewarm water. DO NOT USE HOT WATER. A physician should see the patient promptly if the cryogenic “burn” has resulted in blistering of the dermal surface or deep tissue freezing.
INHALATION :
prompt medical attention is mandatory in all cases of overexposure. rescue personnel should be equipped with self-contained breathing apparatus.
9.4) HAZARD:
1)What happens to ammonia when it enters the environment?
Because ammonia occurs naturally, it is found throughout the environment in soil, air, and water.
Ammonia is recycled naturally in the environment as part of the nitrogen cycle. It does not last very long in the environment.
Plants and bacteria rapidly take up ammonia from soil and water.
Some ammonia in water and soil is changed to nitrate and nitrite by bacteria.
Ammonia released to air is rapidly removed by rain or snow or by reactions with other chemicals.
Ammonia does not build up in the food chain, but serves as a nutrient source for plants and bacteria.
2) How might I be exposed to ammonia?
Everybody is regularly exposed to low levels of ammonia in air, food, soil, and water. Ammonia has a strong irritating odor that people can easily smell before it may cause harm.
If you use ammonia cleaning products at home, you will be exposed to ammonia released to the air and through contact with your skin.
If you apply ammonia fertilizers or live near farms where these fertilizers have been applied, you can breathe ammonia released to the air.
You may be exposed to ammonia from leaks and spills from production plants, storage facilities, pipelines, tank trucks, and rail cars.
You may be exposed to higher levels if you apply ammonia fertilizers or live near farms where these fertilizers have been applied.
You may be exposed to high levels if you go into enclosed buildings that contains lots of animals (such as on farms).
3)How can ammonia affect my health?
No health effects have found in humans exposed to typical environmental concentrations of ammonia. Exposure to high levels of ammonia in air may be irritating to your skin, eyes, throat, and lungs and cause coughing and burns. Lung damage and death may occur after exposure to very high concentrations of ammonia. Some people with asthma may be more sensitive to breathing ammonia than others.
Swallowing concentrated solutions of ammonia can cause burns in your mouth, throat, and stomach. Splashing ammonia into your eyes can cause burns and even blindness.
4)Has the federal government made recommendations to protect human health?
The Occupational Safety and Health Administration (OSHA) has set an acceptable eight-hour exposure limit at 25 parts of ammonia per one million parts of air (ppm) and a short-term (15 minutes) exposure level at 35 ppm.
CHAPTER
10
CONCLUSION
From this project we envisage the practical work going in the chemical plants.some
of the practical espects of the chemical engineering we have putted it nicely in this
project prior to which we don’t have any practical experience.
Our practical view about the chemical plant is align somewhat by doing the project.
By perfuming the calculation of material balance , energy balance,in which how we
Put into practice is cleared. how the chemical plants operation runs on the basis of
calculation is totally envisage now.
CHAPTER
11
BIBLOGRAPHY
1) Perry, R.H. and Green D. , Perry’s Chemical Engineer’s Handbook, McGraw-Hill book company, ed. 8th, pg no. 16-61 to 16-64, 20-57 to 20-62.
2) George T. Austin, Shreve’s Chemical Process Industries, Fifth Edition, Nitrogen Industries.
3) K.A Gavhane,introduction to process calculation,18th edition,nirali prakasan.
4) B.I BHATT ,S.M VORA,stoichiometry 4th edition tata mcgraw-hill publishers
5).John J. Mcketta and William Aaron Cunningham, Encyclopedia of Chemical Processing And Design, Volume-2, Adsorption design.
6). IFFCO ‘ Indian Farmers Fertilisers Cooperative Limited, Ammonia Plant Manual.
7)Prof. M.N. Vyas, Safety and Hazards Management in Chemical Industries, Atlantic publishers and distributors ltd
8).S.B. Thakore, B.I.Bhatt, Introduction to Process Engineering and Design, Tata McGraw Hill Education Pvt. Ltd.(design of adsorber)