Ammonia synthesis

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PowerPoint Presentation:

Ammonia Synthesis Section Presented to: ISO & Training Department Of DH Chemicals Limited Presented by : Farhan Akhtar Institute Of Chemical Engineering And Technology University Of The Punjab

Ammonia Unit:

Ammonia Unit Main Sections Of Ammonia Unit: Reforming Section Catacarb Section Synthesis Section

Synthesis Section:

Synthesis Section Comprises of the following 5 units: Methanator Synthesis Compressor Molecular Sieve Synthesis Converter Compression and refrigeration Section

Main Equipments In Synthesis:

Main Equipments In Synthesis 116-F Knock out drum 1136-C & 1104-C Heat exchangers 106-D Methanator 114-C & 115-C Heat exchangers 104-F Suction Drum(knock out drum) 1103-J Synthesis gas compressor 116-C &129-C Heat exchangers 1109-DA/DB Molecular Sieve 121-C Heat exchanger 1105-D Ammonia convertor

Synthesis Loop:

Synthesis Loop

Knockout Drum (116-F):

Knockout Drum (116-F) The purpose of knock out drum is to remove any moisture content or traces of catacarb solution coming out of the absorber. HLA-39 is a high level alarm which is used to notify about the high level of condensate in 116-F


Methanator Operating Conditions: Inlet Temperature 600  F Outlet Temperature 687  F Inlet Pressure 385 psig Pressure Drop 3-5 psig Catalyst Type Nickel based (in tablet form) Carbon Oxide Composition at Inlet % Outlet % CO 2 1000ppm < 10ppm CO 0.6 (mole percent) 0%

Reactions inside Methanator:

Reactions inside Methanator CO + 3H 2 CH 4 + 3H 2 O + Heat CO 2 + 4H 2 CH 4 + 2H 2 O + Heat

Process Description:

Process Description The temperature of the gases entering the Methanator is increased to 600 degree Fahrenheit. 1136-C & 1104-C are used for this purpose. HCV-13 is a forcing valve which is used to control the temperature of the feed gas entering in the Methanator.


Continued…. Both the reactions are highly exothermic and that is why, Methanator has high temperature actuated, feed shut off valve. this feed shut off valve is actuated at 750 degree Fahrenheit. In case of actuation, the feed is vented to atmosphere. Another problem associated with Methanator is the formation of Nickel Carbonyl Ni(CO)4 . Its formation is favored by low temperature and high pressure.


Continued…. Methanator Effluent : H 2 74% N 2 24% CO 2 7ppm Methanator Vessel Material of construction is 1.25 Cr- 0.5Mo Design Temperature 450 o C ( 850 °F ) From Methanator , syn gas at temp 687 ̊F is cooled up-to 105 o F in 114- C & 115-C. From there it is transferred to 104-F(suction drum) which will remove condensate , before sending it to Syn gas compressor.

Synthesis Compressor(1103-J):

Synthesis Compressor( 1103-J) Operating Conditions: Normal speed 10200rpm Operating speed 83%(8700rpm) to 109%(11400) of designed speed of 10470rpm.

Synthesis Compressor(1103-J):

Synthesis Compressor( 1103-J) It consist of two Sta ges 1 st Stage(low pressure) 2 nd Stage(high pressure)

1st Stage Synthesis Compressor:

1 st Stage Synthesis Compressor Operating Conditions: inlet pressure 350 psig outlet pressure 910-946psig Inlet temp. 105 °F Outlet temp. 350 °F 1 st stage synthesis compressor takes suction from the suction drum(104-F), in which demisting pad is used to remove the moisture content present in the syn gas.

PowerPoint Presentation:

Operating Conditions: Inlet pressure 880psig outlet pressure 1980-2150psig Inlet temp. 46 °F Outlet temp. 142 °F 2 nd stage synthesis compressor takes suction from molecular sieve unit (48522 #/hr) recycle from Ammonia refrigeration unit (348450#/hr)(2 mole % NH 3 ) At outlet the syn gas is 432960 #/hr 2 nd Stage Synthesis Compressor

Problems Associated With 1103-J:

Problems Associated With 1103-J One of the biggest problem that can happen to any compressor is surging. What is surging? “Surging is a to and fro motion of fluid in the compressor which results as the pressure at the discharge becomes higher than the pressure at the suction.” An easy solution to overcome this problem is to recycle some of the feed from discharge to the suction. FICa-7 is there to keep the LP case out of surge and FICa-8 is there to keep HP case out of surge. 1103-J is a turbine driven compressor. There are two turbines. JAT is a high pressure turbine and it operates on 1500# superheated steam. JBT is a low pressure turbine and it operates at 575# steam. The gas coming out of the HP case is at about 142 °F . Its temperature is further increased to about 275 °F by the convertor effluent gas in 121-C which needs cooling.

Molecular Sieve Driers(1109-DA/DB):

Molecular Sieve Driers(1109-DA/DB) Objective: The purpose of molecular sieve is to remove moisture and carbon dioxides from the synthesis gas leaving the 105-F. Syn gas coming from 1 st stage compressor(1103-J) cools in three steps By preheating methanator feed(1136-C) By cooling water(116-C) By ammonia refrigeration(129-C) then pass through knockout drum(105-F) to remove moisture and then enter into molecular sieve driers


Continued…. Molecular sieve dryer contain two vessels such that one in service and other under regeneration. And then passes through molecular sieve filter(1109-LA/LB) before entering HP case of the syn gas compressor. Molecular sieve Desiccant Sodium Alumina Silicate (Na 2 O Al 2 O 3 SiO 2 ) . The desiccant in molecular sieve is 368 ftᶟ desiccant loaded in each vessel- bed height of 15.5 ft.

Ammonia Convertor:

Ammonia Convertor Operating conditions Inlet temp. 275 ° F Outlet temp. 616 ° F Temp. in catalyst beds 680-986 ° F Design pressure 2240 psig Operating pressure 1963 psig Pressure drop 28 psig

Ammonia Convertor:

Ammonia Convertor 3H 2 + N 2 2NH 3 + heat At higher temperatures the equilibrium percentage of ammonia will be too low while at lower temperatures the rate of reaction will be too low. Converter Design pressure is 2240 psig and normal design operating pressure is about 1963 psig. Temperatures in the catalyst beds are in the range of 680 to 986 O F. Promoted iron catalyst containing small amounts of non-reducible oxides.

Ammonia Converter Catalyst:

Ammonia Converter Catalyst KM1R and KM1 nominal size 1.5 – 3.0 mm Unreduced catalyst (KM1) - 90% of iron oxide (Fe 3 O 4 ), the remainder being non-reducible oxides, mainly CaO , K 2 O and Al 2 O 3 (promoters) Reduction of Iron oxide to free iron Pre-reduced catalyst (KM1R) produced by reduction and subsequent stabilization by skin oxidation.


Continued….. 280 Kg / Ton Catalyst reduced (Unreduced catalyst) 28 Kg / Ton Catalyst reduced (pre-reduced catalyst) Normal catalyst life 10 – 15 years – depends on poisons and operational temperatures Catalysts can be operated up to 1004 – 1022 O F Oxygen compounds like CO, CO 2 and H 2 O are poisons. Mild poisoning is temporary and activity can be restored. Sulphur and Phosphorous compounds are permanent poisons.

PowerPoint Presentation:

Basically Synthesis gas introduced is divided into 5 streams . Streams entering via MICe-503 & MICe-505 are called shell- cooling streams or main stream. Streams entering via MICe-502 & MICe-504 called quenches are introduced from the top of the convertor The fifth one is called the cold shot and it is used to provide the exact temperature for first catalyst bed. It is provided from the bottom of the converter. Process Description

S200 Ammonia Converter:

S200 Ammonia Converter


Radial flow type converter lower heat exchanger, two adiabatic catalyst beds and an inter bed heat exchanger The main gas stream is introduced into the converter through the two main inlets (A) at the top of the converter and passes downward through the outer annulus between the basket At the bottom of the converter, the main gas stream flows to the shell side of the lower heat exchanger and is heated to the reaction temperature by heat exchanger with the converter effluent as it leaves the lower catalyst bed. At the shell side exit of the lower heat exchanger feed gas is mixed with the cold shot stream to obtain the correct inlet temperature to the 1 st catalyst bed Continued…..


Continued…. Mixed with Quench gas passing through the tubes of inter bed heat exchanger Gas flows through the first bed radially Cooled through Inter bed exchanger Gas enters 2 nd catalyst bed The temperature inlet to the 2 nd catalyst bed is controlled by adjusting the quench gas rate. Gas is then cooled in the LHE and then flows through the outlet nozzle. Start up heater for converter heating.

Factors Influencing Converter Reaction:

Factors Influencing Converter Reaction Effect of temperature Effect of pressure Effect of space velocity Effect of Hydrogen to Nitrogen ratio Inert gases Synthesis gas rate

Hydrogen To Nitrogen Ratio:

Hydrogen To Nitrogen Ratio A H 2 /N 2 of close to 3:1 in the make-up gas is required in order to keep the H 2 /N 2 3:1 in the gas circulating in the synthesis loop. A small variation in this ratio of the make-up gas will have a relatively large influence on the gas composition in the loop. If the ratio in the loop becomes < 2.6 or > 3.2, the reaction rate in the converter will decrease, and the temperature will tend to decrease while the pressure will increase at a constant make-up gas addition. If measures are not taken to correct the ratio in the loop, the reaction may eventually stop, and the converter will cool down rapidly. Gas Composition

Gas Composition Continued…:

Gas Composition Continued… Inert Level-Purge Rate: The make-up synthesis gas and the recycle gas contains hydrogen ,nitrogen, methane and argon. The methane and argon are inert and tend to accumulate in the synthesis loop. The effective pressure for ammonia synthesis is the partial pressure of H 2 & N 2 , inert in the system lower this effective pressure and retard the production Inert are removed in two ways Some inert are dissolved in the product. But the bulk of the inert is removed by purging some re-circulating gas. The inert level should be selected on the basis of optimization of the product yield versus power consumption of the make-up gas compressor.

Gas Composition Continued…:

Gas Composition Continued… Ammonia Concentration at Converter Inlet: Variation of the ammonia concentration at converter inlet has a considerable effect on the synthesis reaction. A decrease of the ammonia conc. at converter inlet will favors the synthesis reaction.

Recirculation Rate:

Recirculation Rate The re-circulating gas depends on the loop pressure and the rotational speed of the synthesis gas compressor. Normally, the loop should be operated at the maximum recirculation rate.

Loop pressure and purge rate:

Loop pressure and purge rate In the normal operation, the purge rate is kept at a constant rate, where the pressure is itself adjusting in accordance with the load. The purge gas rate should be adjusted in a manner that the optimum inter-relationship b/w the power consumption of the synthesis gas compressor and the product yield is achieved.



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