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De-Bottlenecking of RCF Thal Facility
G N Tatwawadi and Prakash Shankar. The ammonia plants at RCF Thal were revamped phase wise such as to increase capacity and reduce specifi c energy consumption. This article describes the approach towards revamp, execution methodology and the results obtained. This revamp is aimed to contribute towards increasing urea availability while reducing dependence on imports.

Thal Fertiliser complex is located at Thal-Vaishet, in the coastal belt of western India facing the Arabian sea about 25 km. south of Mumbai across the sea and approximately 100 km. away from Mumbai by road. It is connected by railway from Apta-Panvel.

RCF is one of the largest producers of urea in India with manufacturing sites at two locations, Mumbai and Thal. It is among the top ten Public Sector Units (PSUs) having Case Study: De-Bottlenecking of RCF Thal Facility T status of ┬MINIRATNA╩ organisation and is consistently PROFIT making organisation. Both units are certified for Integrated Management System ISO-9001, ISO-14001 and OHSAS- 18001. Thal unit of RCF is the first Fertiliser complex to utilise Bombay High Offshore Natural Gas.

Performance at RCF Thal
Highest ever urea production of 19.33 lakhs million tonnes was made in the year 2008-09 with mix feed of gas and naphtha in ammonia plant. Lowest ever specific energy consumption of 6.297 mkcal/mt of urea and 8.864 mkcal/mt of ammonia was achieved in the year 2009-10 with natural gas as feed to primary reformer in ammonia plant.

Synopsis of Revamp Project
The Government╩s policy aims at achieving the maximum possible degree of self sufficiency in production of nitrogenous fertiliser based on utilisation of feedstock as NG/RLNG. The primary consideration and goal of the pricing policy is to encourage efficiency parameters of international standards based on the most efficient use of feedstock, state-of-art technology and also ensure viable rate of return to the units. Government has started implementing this policy in stages. Due to the new pricing policy, it has become imperative for every fertiliser unit to be very cost effective to stand in the competitive market. Keeping this in view, RCF management decided to revamp the ammonia plants at Thal unit to reduce energy consumption and to enhance production. RCF Thal had stopped using naphtha in the year 2009 due to availability of D-6 KG basin gas from M/s RIL. This gas being lean in nature contains less carbon as compared to naphtha. It has reduced CO2 production thus severely affecting urea production. To enhance urea production capacity, existing Thal ammonia plants are being revamped from 1500 mtpd x 2 to 1750 mtpd x 2 with increased CO2 production to produce 6100 MTPD urea. Expected reduction in specific energy consumption in ammonia plant is by 0.6 MKcal/MT and in urea plants by 0.35 MKcal/MT.

Revamp Schemes for Thal Ammonia plants
• Replacement of Primary Reformer tubes, pigtails and catalyst
• Primary Reformer Burner modification, NG coil modification and new plate type Combustion Air Pre heater installation in place of fin type.
• Addition of GV System in Benfield for CO2 removal.
• Additional S-50 Converter and Loop Boiler to enhance conversion of ammonia and steam production.
• MP Stripper in place of LP stripper.
• Revamp of Synthesis Gas Compressor Turbine to improve efficiency.
• Replacement of BFW pumps, turbines from backpressure to condensing type using LP Steam.
• Replacement of Cooling tower Pump Turbines from MP steam condensing type to LP steam Condensing type.

Revamp Schemes for Urea Unit-31
From existing three numbers of urea units, it is possible to produce 5700 MTPD (1900 MTPD each) on consistent basis. Hence, only one urea unit (Unit-31) is selected for capacity revamp. After revamp, Unit-31 plant production will increase from 1900 MTPD to 2300 MTPD. Total production capacity after revamp will be 6100 MTPD.

Modifications required for enhancing Urea-31 Plant Capacity are:
• Replacement of one new HP ammonium Carbonate Pumps (P2) with higher capacity.
• One additional new HP Ammonia Feed Pump (P1).
• One additional new Passivation Air compressor (K3).
• Higher capacity Third Inter stage Cooler (E26) of CO2 compressor.
• Third Inter stage Separator (MV18) of CO2 compressor.
• Installation of a New Ammonia Pre-Heater.
• Revamping the existing Vacuum system by addition of new condensers and ejectors.

Project Cost
Approved project cost of the project is Rs. 488.75 crore and ZERO date of the project is 20th March 2009.

Revamp will be completed by December 2012. After commissioning, the production of urea plant is likely to upscale to 20 lakh MT per annum.

Specific Energy consumption for urea is expected to come down to 5.9 MKcal/MT.

SCHEME IMPLEMENTATION DETAILS Ammonia Plant
1. Synthesis gas turbine revamp:
The HP turbine rotor along with diaphragm of Synthesis Gas Compressor (SGC) was replaced with modified design in the year 2009-10 and 2010-11 in Ammonia Line-II and Line-I respectively to reduce steam consumption.

By revamping the turbine, machine is able to take additional load required to produce more than 1900 MTPD of Ammonia.

Steam saving achieved are 13.5 MT/ Hr in Line II and 10.0 MT/Hr. in line I respectively.

2. Primary reformer tubes, pigtails and catalyst has been replaced with a new one. Tubes were in service since April 1996-97 in Line I and Line II respectively. Catalyst was in operation since April 2007 in both streams. Furnace top roof ┬Z╩ blocks, waste heat section and furnace wall above the 6th row burner were replaced. The new catalyst supplied by M/s HTAS is a triple-decker catalyst similar to previous charge.

3. New modified burner with air cones for primary reformer: Total 576 numbers of old burners along with air cones of each line were replaced with new modified burners and cones. In Line-II, out of 576 numbers of burner blocks, 362 numbers of damaged burner blocks were also replaced. The purpose of burner modification was to handle recycle synthesis gas to be fired in primary reformer furnace such that the front end of ammonia plant can be operated at higher load. Now front end of ammonia plant can be operated at higher load to produce more CO2. The design maximum Burner pressure is 2.0 Kg/cm2 to take care of the partial recycled synthesis gas in reformer.

4. Replacement of the combustionair preheater coil (E205) in Waste Heat Section of Line-I/II with Plate-type exchangers was done to recover heat from flue gas such as to reduce temperature of flue gas from 175 degree Celsius to 130 degree Celsius. Line I CAPH was replaced in May-June-11 and that of line II was replaced in Oct.-Nov 11.

5. Modification of natural gas pre heater coil (R204 A/B) was carried out in Line-I in May-June.11 and in line II during Oct.-Nov.2011 annual turnaround. The net reduction in pressure drop at 45.72 TNCH primary reformer load was 1.4 Kg/cm2. Before modification of the coil, there was a limitation to increase the feed load in the primary reformer. After modification of NG Preheater coil (E 204 A/B), it is now possible to increase the feed to primary reformer (50.376 NM3/ Hr designed for 1945 MTPD in the front end) without any changes in reformer tube dimension.

6. Modification of boiler feed water header P605 and P601 was carried out to have flexibility in operation BFW Pumps as required.

7. Provision has been made to fire excess synthesis gas in primary reformer as fuel. Now it is possible to increase front-end load for more CO2 production.

8. Revamp of CO2 Removal System to Giammarco Vetrocoke (GV) system was implemented in Ammonia line-II during Oct-Nov 2011 annual turnaround. In order to improve energy efficiency and increase CO2 production capacity, the existing Benfield section was revamped to GV two stage regeneration systems. In this system, Glycine is an additive that will increase CO2 absorption capacity. Low-pressure steam consumption will be reduced from 35 MT/Hr. to 13 MT/Hr (design), thus reducing energy consumption.

Equipments Installed
LPGV Stripper, CO2 booster compressor, GV solution - DMW preheater, LP steam reboiler, Lean solution pump, Separator OH LP GV stripper along with LP steam ejector and condensate pumps OH LP GV Stripper etc. Existing Benfield Regenerator (F301) bottom most bed packing (previously loaded with IMTP 50) was replaced with IMTP 40. New nozzles and take off trays for rich and semi lean solution were installed below 2nd bed and 3rd bed. A side stream of rich solution extracted from the top of regenerator, Semi lean solution extracted from intermediate tray and Lean solution from the bottom of the Regenerator ((F301) is collected in new LP GV stripper (F1351) at different levels. Semi lean solution extracted from intermediate tray of F301 is flashed and fed to LPGV stripper. The existing Flash vessel (B305) receives liquid from LPGV stripper semi lean take off tray is pumped to CO2 absorber (F302) by P1301 A/B/C. Lean solution extracted from the bottom of F301 is flashed in LPGV (F351) below the semi lean solution takeoff tray and collected in the bottom and cooled by DMW preheater (E352 A/B) and fed to absorber top with new lean solution pump (P353 A/B).

The system was successfully commissioned and CO2 production was lined up to urea plant on 28th November 2011. With the implementation of the above scheme in Ammonia line-II, total CO2 production both ammonia plants has gone up and urea production has increased from 5550 MTPD to 5800 MTPD. Installation of Additional S-50 Synthesis Converter (R502) along with new loop boiler (implemented in Line-II in Oct.-Nov.11)

In order to increase the energy efficiency of the ammonia synthesis loop an S-50 converter (R502) has been installed in the downstream of the existing converter. The increase in ammonia concentration exit, the new converter has resulted in decrease in loop pressure and lower circulation rate. This has given substantial savings on the synthesis gas compressor and refrigeration circuit. A new loop boiler (E501 A) has been installed between the converters in order to maintain the inlet temperature of new converter (R502). A bypass on E501A controls the inlet temperature to R502. The existing loop boiler (E501B) is maintained in downstream of S-50 converter. After revamp design synthesis loop pressure and recycle flow are 180.6 Kg/cm2 and 641.865 NM/Hr respectively. S-200 and S-50 outlet ammonia concentrations are 18.85 per cent and 23.05 per cent respectively. Synthesis section of Line II Ammonia plant was commissioned and the production started on 30th November 2011. S-50 converter outlet composition has reached to 22.8 per cent with recycle flow of 680 Nm3/hr at production load of 1900 MTPD. For erecting the converter, a special crane was brought from Baroda by road transport and commissioned at Thal site. After implementation of above schemes (Phase I & II), highest ever daily ammonia production achieved is 3675 MTPD with specific energy consumption of 8.55 Mkcal/MT. Daily urea production achieved is 5800 MTPD with Specific Energy consumption of 5.94 Mkcal/MT. Based on available data till date the effect of revamp phase-I and phase-II can be seen in following graph:

Conclusion
The implementation of Phase-I and Phase-II schemes has resulted in achieving the following objectives:

• Attaining daily Ammonia production to the tune of 3650 MTPD.
• Reduction in daily specific energy consumption of ammonia plant from 8.85 MKCal/MT to 8.6 MKcal/MT.
• Attaining urea production from earlier 5400 MTPD to 5800 MTPD.
• Daily urea specific energy consumption has decreased from earlier 6.25 to 6.0 MKcal/MT.
On successful completion of all the revamp activities, the urea production is expected to increase 6100 MTPD and specific energy consumptions of ammonia and urea are expected to come down to 8.1 MKcal/MT and 5.9 MKcal/MT respectively.