INTERNSHIP REPORT ON PRODUCTION PROCESSES OF AMMONIA AND UREA AT

NFCL

Presented by:

R. Sitarama Chandra murthy.Dasari nithin prabhakar.

AMMONIA PRODUCTION

Production steps:The various steps involved in the production of synthesis gas and ammonia are:

1. Natural Gas Supply

2. Desulphurisation section

3. Reforming section

4. Primary Reformer

5. Secondary Reformer

6. CO conversion section

7. CO2 removal section

8. Methanation

9. Process condensate stripping section

10. Ammonia synthesis section

11. Refrigeration section

12. Ammonia absorption section

13. Purge gas recovery unit

AMMONIA PLANT:

• INTRODUCTION:- N.F.C.L (Nagarjuna Fertilizers and Chemicals Limited) manufactures the product Urea (NH2-CO-NH2).

• The plant is based on the latest technology from M/s Snamprogetti, Italy for the Urea process and Halder topsoe(Denmark) for ammonia process, with an installed capacity of 1500 Mt/day for each stream, later it has been increased to 1800Mt/day for each stream through the process of revamping.

• The Industry has two Ammonia plants, two Urea plants, Bagging Plant and Utilities & Power Plants. The Raw materials used for manufacturing the Ammonia and Urea are:- 1) Natural Gas - From Krishna Godavari basin through GAIL.2) Natural air - Atmosphere.3) Water - From SAMALKOT through a canal.

TECHNICAL FEATURES:Installed Capacity : 2 x 1500 MT Urea / Day

2 x 900 MT Ammonia / DayRevamped Capacity :2 x 2325 MT Urea / Day

2 x 1325 MT Ammonia / Day

• BAGGING PLANT:• 1 BAG of urea contains = 50 Kg• Each empty bag weighs= 130gms• 1 stream contains 250 tonnes of urea in 8hrs.• In NFCL they use 6 streams total which packs 1500 tonnes of urea in 8hrs.• That is about 30000 bags of urea are packed in 8hrs and in total 90000 bags

in 1 day.

• Fig: Catalyst used

NH3 MANUFACTURING PLANT

PRE-DESULPHURIZATION:• Natural gas contains sulfur compounds of types R-SH, R1-S-R, R-S-S-R1 etc• These compounds are removed by hydrogenation process where H2 is added. So, for liquid

natural gas to react with hydrogen it is to be converted to gaseous state and thus it is sent to fired heater and then into HYDROGENATOR.

• H2

PRE-HEATING FURNACE HYDROGENATOR (F-203) (R-201)

• The reactions that take place in hydrogenator are:

• R-SH + H2 R-H + H2S• R-S-RI + 2H2 R-H + R1-H +

H2S• R-S-S-RI + 4H2 R-H + R1-H

+ 2H2S• CATALYSTNIMOX(Nickel-

Molybdenum)• OPERATING

CONDITIONS:380OC & 24KSC

Fig:Total Desuphurization Section (Hydrogenator & absorbers)

• FINAL DESULPHURIZATION:

• So, S is removed to a large extent as H2S, to strip off the H2S present in the product, the stream is sent into the stripper where product stream falls from the top and the steam from the bottom.

• 0.5 ppm of sulfur is present and thus is to be further removed because S acts as a poison to the catalyst in the reforming section.

• So, the product obtained is sent into the final desulphurization unit for further removal of S.

• So the H2S formed now is sent into the reactors where ZNO beds are present. The sulfur removal inside the beds takes as follows:

ZNO + H2S -> ZNS + H2O

Zno Zno

R202A R202B

Catalyst: Ni based unreduced catalyst R-67-7H at the bottom..R-67-7H is unreduced and used in tubular reformers downstream a prereformer or for steam reforming of light feedstocks such as natural gas. For reforming of feedstocks ranging from heavy natural gas to LPG . R-67-7H is delivered in a prereduced version for fast start-up.

• Pre reduced catalyst R-67R-7H at topBy using the R-67R-7H in the top of the tubes, the reforming process is initiated immediately when exposed to process gas. The hydrogen generated in the top layer rapidly activates the catalyst in the lower part of the tube, and this easy activation greatly minimizes the start-up time.

REFORMING SECTION:

• The process gas thus obtained is sent to the ADIABIATIC PRE-REFORMER where high carbon chains of naphtha are broken into low carbon chains by cracking and this gas is sent into REFORMING SECTION.

• Reforming means conversion of hydrocarbons to CO2 with the help of steam. This takes place at high temperatures since it is a endothermic reaction.

• The reactions that take place are called as shift reactions.• CH4 + H2O -> CO + 3H2

• CH4 + 2H20 -> CO2 + 4H2

• CATALYST – Ni based catalyst. • TEMPERATURE - The temperature required is nearly 950oC & 30.5KSC.• Reaching this temperature at once is very difficult and thus it is done in 2 stages: 1.Primary Reforming 2.Secondary Reforming

PRIMARY REFORMER:• This reformer contains 190 tubes in 2 parallel sections.• Each section contains95tubes, divided into 5zones, i.e, each zone contains 19tubes.• The furnace operates with side firing of fuel gas on both sides of each row of tubes.• These tubes are filled with Ni catalyst.• Super heated steam along with natural gas is sent into small tubes.• Nearly 86% conversion takes place. Thus the product stream contains

C0+C02+CH4+H20.

z1 z2 z3 z4

5z

Each 19 tubes

Firing inside Primary Reformer

SECONDARY REFORMER:• Product stream along with air is sent inside the reformer where it is heated to 945oC

for the rest 14% conversion of CH4.• The off gases that are evolved during the stripping of H2S gas are used as a fuel to

secondary reformer for maintaining high temperatures.• The product stream now contains only CO, CO2, H2 and AIR. In order to convert CO to

CO2 it is sent into the CONVERTER via WASTE HEAT BOILER.• This waste heat boiler recovers the heat from the product stream and is used for

rising temperature.

secondary reformer 

HT CO(or SHIFT) CONVERTER: • From waste heat boiler the process gas enters High Temperature CO converter. This is

maintained at 360oC.• Although CO conversion to CO2 takes place at low temperatures this converter is used

in order to increase the speed of reaction.CO + H2O CO2 + H2 + Heat

Catalyst: copper promoted iron oxideOperating conditions: 3600C& 29.8 Kg/cm2g

LT_CO(OR SHIFT) CONVERTER:• The stream from HT CONVERTER enters the LT CONVERTER and the CO formed in the

process is converted to CO2. • This is maintained at 140oC. Catalyst: Catalyst consisting of oxides of copper, zinc and

aluminum.Operating conditions: It will be operated between 200 to 2180C.

Fig: High temperature shift converter 

Fig: Low temperature shift converter

CO2 REMOVAL SECTION:• CO2 that is present is to be separated and thus it is sent into a tower where it is made

to mix with a solution called GV SOLUTION .• GV SOLUTION (GIMMARCO – VETRACOKE SOLUTION) whose constituents are K2CO3,

V2O5, DEA and GLYCINE.• V2O5 acts as the catalyst and DEA, GLYCINE are the initiators of the reaction.• The operating conditions are 2.5 KSC, 250oC.• The reaction that takes place is:K2CO3 + H20 + CO2 -> 2KHCO3

SEMI-LEAN GV SOLn

Lean GV

GV+ CO2

Components of GV Solution:K2CO3 = SolventGlycine = ActivatorV2O5 =corrosion InhibitorDEA = promoter

CO2 REMOVAL SECTION

CO2 REGENERATOR and METHANATOR:• This KHCO3 is to be stripped for removing the CO2 from the GV SOLUTION.• This stripping is done both at high pressures and low pressures.• High pressure regeneration at 1 KSC is done where steam is made to flow counter-currently to KHCO3 solution.• This helps in CO2 stripping off. Traces of CO2 that are present are also to be stripped and thus they are sent into the low pressure regenerator which is made to work at 0.1 KSC.

• This process gas is now made to pass through the METHANATOR so that traces of CO2 left out is converted into CH4 once again and this is called as “reverse shift reaction”.• CO2 + 4H2 -> CH4 + 2H20

NH3 SYNTHESIS SECTION:• .• the reaction is exothermic , so low temperature is favorable.• Since the no. of moles decreases high pressure is favorable. • H2/N2 ratio is maintained at 2.78:1 .• The output of absorber section i.e; from final separator ,it is passed to 4 stage compressor.• Then purge is taken, and is passed to 8heat exchangers connected in series and to ammonia reactor.• And the formed ammonia is collected in V-502 , we get pure ammonia.

4 STAGE COMPRESSOR

Fig: Ammonia Synthesis Reactor

Reaction:• N2 + 3H2 2NH3 +Heat• H2 / N2 ratio is maintained at

2.78:1• Catalyst: First bed KM1R

catalyst Second bed KM1 catalyst.• Operating conditions:

131-141 Kg/Cm2g & 360 - 5200C

KM1R Ammonia synthesis catalystIt is a prereduced iron-based ammonia synthesis catalyst containing a number of carefully selected promoters.Application.itis used in the majority of the world’s ammonia converters to convert synthesis gas containing hydrogen and nitrogen into ammonia.

To produce ammonia from a variety of hydrocarbon feedstocks ranging from natural gas to

heavy naphtha using Topsøe’s low energy ammonia technology.

AMMONIA SEPERATION:

Purpose: To separate the ammonia from the unconverted process gas. It

included 2 sections.

 

1) Ammonia Refrigeration 2) Ammonia absorptionAmmonia Refrigeration:

The refrigeration section is used to liquefy gaseous Ammonia and consists of a compressor unit, a condenser, an accumulator and number of chillers. Liquid NH3 flows from the NH3 accumulator, to the NH3 heater, which serves to heat Ammonia sent to the Urea Plant.

Ammonia Absorption:

Ammonia produced in the Ammonia Synthesis Converter separated from unreacted gas mixture in Ammonia Separator.

Fig: Ammonia separation

Purge Gas Recovery Unit: 

Purpose: To recover the H2 from the purge gas

Fig: purge gas recovery unit

Production of UREA

Properties of urea• Urea is a white, odorless, hygroscopic solid. It is non-corrosive.

The Urea production takes place through the following main operations:

• Urea Synthesis and High Pressure Recovery

• Urea purification in the medium, low and pre-vacuum pressure

recoveries.

• Urea concentration

• Urea Prilling

• Bagging

UREA SYNTHESIS AND HIGH PRESSURE RECOVERY:

Purpose: synthesis of urea

2NH3 + CO2 NH2COONH4 (Ammonium carbamate)

NH2COONH4 NH2CONH2 (Urea)+ H2O

CO2 and NH3 obtained in ammonia plant are sent into UREA

PLANT. Since the reaction requires high pressures both the

reactants are compressed.

Urea is produced by the synthesis of liquid ammonia(240 KSC, 135°c) and gaseous carbon dioxide. The first reaction occurs rapidly and is completed, while the second reaction occurs slowly and determines the reactor volume. The fraction of ammonium carbamate that dehydrates is determined by the ratio of the various reactants, the operating temperature and the residence time in the reactor.

The molar ratio of ammonia to carbondioxide is in the range of 3.3-3.6 to 1. The molar ratio of water to carbondioxide is in the range of 0.50-0.70 to 1.

UREA PURIFICATION IN THE MEDIUM, LOW AND PRE-VACUUM PRESSURE RECOVERIES:

Urea purification takes place in three stages at decreasing pressures as

follows:

1st stage at 18.0 kg/cm2 pressure

2nd stage at 4.50 kg/cm2 pressure

3rd stage at 0.35 kg/cm2 pressure

M.P Decomposition and separation: Purpose: To increase the concentration.

Description: The solution with a low residual CO2 content, leaving the bottom of the stripper is expanded to a pressure of 18 kg/cm2 and enters the medium pressure decomposer which is a falling film type.

L.P. Decomposition and separation:Purpose: To increase the urea concentration in the solution.

Description: The solution leaving the bottom of medium pressure decomposer is expanded to 4.5 ksca pressure and enters the low-pressure decomposer at 4 KSC, 145ºC, which is also a falling film type. Where 72% urea is obtained.

Pre vacuum concentrator:Purpose: To increase the urea concentration. Water will be evaporated from the urea solution.

Description: The solution leaving the bottom of low-pressure decomposer is expanded to 0.35KSCg pressure and enters the vacuum pre-concentrator which is also a falling film type.

permits to concentrate the urea solution from about 70-75% to about 85-88 % by weight

UREA CONCENTRATION SECTION:

It is necessary to concentrate the Urea solution up to 99.8 % wt in order to prill Urea. A vacuum concentration section in two stages is provided to accomplish this concentration.

• The urea solution is sent to the first vacuum concentrator, operating at a pressure of 0.35ksca.

• The mixed phase coming out enters the gas liquid separator, from where vapors are extracted by the first vacuum system, while the solution enters the second vacuum concentrator, operating at a pressure of 0.03ksca.

• The two concentrators are fed by LP steam. The mixed phase coming out enters the gas liquid separator, from where vapors are extracted by the second vacuum system.

• Water obtained is condensed and then sent into waste water tank. It contains 5% Ammonia and 1% Urea. Molten urea is sent to the prillin tower.

PRILLING SECTION: • The height of the urea prilling tower is 100 meters and 22 meters in diameter. • The molten urea leaving the second vacuum separator holder, is sent to the prilling bucket,

by means of centrifugal pump. • The Urea coming out of the bucket in the form of drops fall along the prilling tower, and

encounters a cold air flow which causes its solidification. The heated air along with a few ppm of urea dust comes out of the prilling tower top to atmosphere.

• The solid prills falling to the bottom of the prilling tower are sent by the rotary scraper, to the belt conveyor, and then to the belt conveyor, from where Urea can be taken either for bagging or to the Silo.

Snam Progetti (Italy) ProcessThis process is based on the principle of the internal

carbamate recycle technique and is commonly called the Snam NH3 stripping process.

The basic difference between the Snam process & the conventional carbamate solution recycle urea processes is the fact that in this case the unconverted carbamate is stripped and recovered from the urea synthesis reactor effluent solution at reactor pressure, condensed to an aqueous solution in a steam producing high pressure condenser, & recycle back to the reactor by gravity.

Part of the liquid NH3 reactor feed, vaporized in a steam heated exchanger, is used as inert gas to decompose & strip ammonium carbamate in the steam heated high pressure stripper.

The reactor operates at about 130 atm & 180-1900C. The stripper operates at 130 atm & 180-1900C.

The stripper off-gas is condensed in a vertical shell & tube condenser, operating at about 130 atm & 148-1600C.

Low pressure steam is produced in the high pressure carbamate condenser. The urea product solution, leaving the stripper & still containing 2-3 % of residual unreacted carbamate, is further degassed in a low pressure decomposition-absorption system.

The recovered ammoniacal solution of ammonium carbamate is pumped back to the reactor.

Snamprogetti process

USES OF UREA

About 56 % of Urea manufactured is used in solid fertilizer.

About 31 % of Urea manufactured is used in liquid fertilizer.

Urea-formaldehyde resins have large use as a plywood adhesive.

Melamine-formaldehyde resins are used as dinnerware & for making extra hard surfaces.

THANK YOU

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