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Recent efforts in energy conservation in ammonia and urea plants


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Recent efforts in energy conservation in ammonia and urea plants

  1. 1. Indian J. Fert., Vol. 4 (12), pp. 17-20 (4 pages) Recent Efforts in Energy Conservation in Ammonia and Urea Plants Ammonia and urea plants have improved their energy efficiency over the years. Improvement in energy efficiency is a result of concerted efforts of the S. NAND industry by implementing various energy saving schemes and adopting efficient and technologies for the new plants. The declining trend in weighted average energy consumption of ammonia and urea plants over the years is the MANISH GOSWAMI testimony to these efforts. The weighted average energy consumption of all The Fertiliser Association of India FAI, House, 10 Shaheed Jit Singh Marg ammonia and urea plants in 2007-08 was reduced by about 30% from the level New Delhi-110067 of 1987-88. The article reviews the development in ammonia and urea industry and the energy conservation efforts so far. The recent energy conservation efforts of the industry are covered in more detail. 1.0 INTRODUCTION development of fertiliser industry in India. Table 1 – Capacity build-up of Commercial production took off in 1951 ammonia plants (for selective years) with first large scale ammonia plant usingI NDIAN AMMONIA AND UREA INDUSTRY has been in existence for more than halfa century. Initial period of development coke oven gas as raw material. It was only after a decade that another ammonia plant Year 1987-88 Ammonia capacity(MMT) 8.6emphasized on indigenisation since came up in 1961 at Nangal using 1990-91 10.0foreign exchange was a scare commodity electrolysis of water as source of 1993-94 10.1and also there was emphasis on self- hydrogen. Major nitrogenous fertiliser 1996-97 11.3reliance. The next phase of development products initially were ammonium 1998-99 12.7witnessed the efforts for improving sulphate and calcium ammonium nitrate. 1999-00 12.0reliability and operating factors. Spiraling It was only in 1959 that first urea plant of 2000-01 13.7energy costs in the decade of 1970’s 70 tonnes per day (tpd) based on once 2002-03 13.4shifted the attention to improvement in through process was commissioned at 2005-06 13.2operating efficiency in the energy Sindri. 2006-07 13.2intensive industry. Energy is a major cost 2007-08 13.2item in the cost of production of ammonia In the beginning, capacity of both theand urea and hence the efforts for energy ammonia and urea plants was less than In the initial phase of development of theconservation intensified in 1980’s and 500 tpd. These plants used turbo fertiliser industry world wide, energycontinued to the present time. FAI has compressors for high pressure efficiency was not a focus area in designbeen monitoring the energy efficiency of reactions. Capacity leap frogged with of plants. This was due to the fact thatammonia and urea plants since mid- the advent of centrifugal compressors. energy in various forms viz. natural gas,1980’s. Status papers were published at A 600 tpd ammonia and matching urea naphtha, electricity, etc. was veryregular intervals reviewing the energy capacity was the norm for several inexpensive. However, then came the oilconservation efforts of the industry and projects in India. Centrifugal shock of the year 1973 when energy pricesresults obtained. Two of these reviews compressors not only enabled large trebled in short time. Designers of the plantpublished were in 2003 (1) and 2006 (2). capacity in single stream, but also paid attention to the energy efficiency asThis paper traces the developments in used waste heat of the plant in form of a parameter in addition to the capital costammonia and urea industry in brief from steam as motive force. This made a of the plant.the old times and reviews the major significant improvement in the energyefforts for energy conservation impacting efficiency of ammonia production. A few modern energy efficient ammoniathe energy intensity of the industry. The Subsequently developments in plants were commissioned in 1984-85 withmost recent efforts of the industry in this technology, catalysts and equipments specific energy consumption figures closearea are covered in more detail. allowed the capacity to increase to 900 to 7.0 GCal/MT of ammonia. These plants and 1350 tpd. Industry is now operating of about 1000 tpd each included one at 2.0 DEVELOPMENT OF a large number of ammonia plants with Court right, Ontario in Canada, Sluiskil in AMMONIA INDUSTRY capacity of more than 1500 tpd and urea Netherlands and at Ludwigshafen in plants of almost 3000 tpd. The build of Germany. Large scale ammonia plants ofHISTORY OF DEVELOPMENT OF AMMONIA ammonia capacity in recent times is 1350 tpd using gas as feedstock also cameindustry in the country runs parallel to the shown in Table 1. up in India around the same time. However, INDIAN JOURNAL OF FERTILISERS December 2008 17
  2. 2. energy consumption of these plants was equipments offered opportunity to all continued even in 1990’s in various units,higher than the plants mentioned above. existing plants old and new to improve there was renewed emphasis on recoveryThis was due to the fact that Indian energy efficiency. Therefore, revamp/ of additional waste heat from the off-gasesproject owners wanted plants with proven retrofit/replacement measures were of reformer furnace. The temperature oftechnology and equipment. This was after implemented as an ongoing exercise. off-gases was brought down to as low asthe experience of poor performance of 150-160ºC from more than 200ºC earlier inplants commissioned in 1970’s with 4.1 Energy Conservation Efforts in the relatively new plants. Along with otheremphasis on experimentation in Ammonia Plants heat integration steps in the ammoniatechnology and indigenization of the plant, these steps reduced energyequipment. Local environmental 4.1.1 Phase I (1980’s) consumption by 0.1-0.2 GCal/MT ofconditions (hot and humid) and ammonia. There was also revamp of CO2configuration of plants also increases the Production of ammonia is the most removal system by way of change to betterenergy consumption by 2-3%. technologically complex and energy solvent, better packing in absorption and intensive process. Ammonia production desorption towers for higher mass transfer 3.0 DEVELOPMENT OF takes about 80% of total energy required efficiency. For example, in one of the units, UREA INDUSTRY for production of urea and other energy consumption was reduced from fertilisers. Hence, there has always been 36,000 KCal/Mol CO2 to 26,000 Kcal/MolDEVELOPMENT OF UREA INDUSTRY RUNS sharp focus on the energy conservation CO2 with change of solvent from ammineparallel to build up of ammonia in the efforts in ammonia plants. The first phase to Urea being the main product for of energy conservation measures in 1980’ssupply of nitrogen, urea plants were included installation of Purge Gas The next generation efforts in energyinstalled along with all ammonia plants Recovery Unit (PGRU) for recovery of conservation included a number ofwith a few exceptions. First large scale (500 hydrogen from the purge gas. All these significant measures. The highlight oftpd) urea plant based on total recycle units were based on cryogenic separation these efforts were change of internals ofprocess was commissioned in 1966 at of hydrogen which was recycled back to synthesis converter in old plants formNeyveli. It was part of ammonia-urea the synthesis loop. Till then, the purge gas axial flow to radial-axial or radial flowcomplex using gasification of lignite as was burnt as fuel in the reformer. This which allowed the use of more activesource of hydrogen for making ammonia. measure alone reduced specific energy catalyst of finer particle size withoutA number of plants with total recycle consumption by 0.15-0.25 GCal/MT of increasing the pressure drop through theprocess were commissioned in the decade ammonia. reactor. This in turn resulted in increaseof 1970’s. Stripping processes were in conversion per pass and thus reducingdeveloped by Stamicarbon and The second most significant the energy consumption in recycle ofSnamprogetti. Most plants commissioned development was availability of reformed synthesis gas. This measure alone savedin 1980’s and 1990’s adopted tubes of better metallurgy than that of 0.20-0.25 GCal/MT of ammonia.Snamprogetti ammonia stripping process HK-40 or equivalent used in mostwith lower steam and power consumption. reformers. The new metallurgy like IN519 Almost all ammonia and urea unitsThese plants consumed steam and power had higher strength and it was possible changed from analog to digitalequivalent to about 1.0 GCal/MT of urea to use thinner wall tubes for the same instrumentation with screen basedcompared to energy consumption of earlier operating condition of temperature in the controls. Installation of Distributedtotal recycle plants equal to or higher than reformer. This allowed larger inner space Control Systems (DCS) and Programmable1.5 GCal/MT of urea. for packing of catalyst and hence higher Logic Controllers (PLC) became the norm throughput. This not only increased the in the decade of 1990’s. Ammonia plants 4.0 ENERGY CONSERVATION reformer capacity but also helped to save designed for 8.0-8.2 GCal brought down EFFORTS energy consumption. their energy consumption to 7.7-7.8 GCal/ MT ammonia.IT I S EARLIER STATED THAT L ATER Other measures included use of solventgeneration plants were designed with low promoters in CO2 removal section, more Major energy conservation measuresenergy consumption in view of escalating heat recovery in the convection zone of implemented in the decades of 1980’s andenergy prices in the 1970’s. However, older reformer furnace, etc. 90’s helped to bring down the energyplants needed to modernize and reduce consumption in existing plants. Table 2energy consumption to remain 4.1.2 Phase II (1990’s) shows the level of energy consumption ofcompetitive. Continuous developments in ammonia plants in 1987-88 and than of theprocess technology, catalyst and design In reformer section, while change to same plants in 1999-2000. Furtherand materials of construction of better metallurgy of reformer tubes improvement in energy efficiency in the18 INDIAN JOURNAL OF FERTILISERS December 2008
  3. 3. existing plants is possible only in small 13.0increments. 12.48 12.5Table 2 – Reduction in energy consumption 12.0 of ammonia plants after implementation of Energy (GCal/MT)energy conservation measures in old plants 11.5 (GCal/MT) 11.0 Feedstock 1987-88 1999-2000 10.5 Gas 9.96 9.60 10.0 Naphtha 12.26 10.56 9.5 Fuel oil 13.92 13.71 8.97 9.0 Total 11.70 11.31 Phase III (2000 onwards) 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 -8 -8 -9 -9 -9 -9 -9 -9 -9 -9 -9 -9 -0 -0 -0 -0 -0 -0 -0 -0 -0 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 19 19 19 19 19 19 19 19 19 19 19 19 19 20 20 20 20 20 20 20 20 Energy prices witnessed a steep climb Yearduring last 5-6 years. At the same timecost of revamp and retrofit measures have Figure 1 – Energy consumption trends in ammonia plantsalso increased multifold during last decadeor so. Increasing cost and lack of Liquid ammonia wash of synthesis gas As a result of the energy conservationincentives in the pricing policy in has helped to remove impurities of CO2 efforts of the industry and addition ofgeneral slowed the investment in and moisture. Discharge from synthesis capacity through more efficient plants, thedebottlenecking and energy saving gas compressor was originally going to 1st weighted average ammonia energy con-schemes. Nevertheless, improvement stage ammonia separator via chillers and sumption of ammonia plant was reducedcontinued to occur with technical then to convertor. After additional from 12.48 GCal/MT in 1987-88 to 8.97 ininnovations in operation and maintenance purification, it is going directly to the 2007-08. The best plant achieved energyand projects with small investment. convertor and thus saving energy in consumption of 7.70 GCal/MT of ammoniaHowever, there are a few units which made chillers. In a separate measure in some during 2006-07. Table 4 gives thelarge investment in energy saving projects units, chilling of make up synthesis gas feedstockwise energy consumption ofwith significant energy saving. has helped to save the compression ammonia plants during 2007-08. Figure 1 Low Temperature Shift (LTS) guard with energy in the synthesis compressor. shows the trends in energy consumptionadditional heat recovery to preheat boiler of ammonia plants over a period of 20 There are numerous small measuresfeed water helped to reduce CO slip from years. implemented by a large number of plants.0.20 to 0.10 % mole percent at the exit of Table 4 – Feedstock-wise energy For example, even feed gas saturation withLTS convertor resulting in energy saving consumption of ammonia plants process condensate has helped toof order of 0.02 GCal/MT in a number of Feedstock Production Energy conserve energy. Most plants areunits. In carbon dioxide removal section, (MMT) consumption operating with the DCS and take full (GCal/MT)change from single to two stage advantage of automation. A number of Gas 9.86 8.49regeneration allowed better heat units have installed Advanced Process Naphtha 0.94 9.85integration. Changing of single stage flash Control (APC). While energy savings are Fuel Oil 1.43 11.72vessel system in regenerator section with small of the order of 0.05-0.1 GCal/MT Overall 12.24 8.975-stage flash vessel with ejectors ammonia, operation of plant becomes veryincluding a mechanical steam compressor smooth with control of most operating 4.2 Energy Conservation Efforts in Ureawas carried out by another unit. One of parameters within the narrow range. APC Plantsthe units has also installed hydraulic also enables the optimization of plantturbine to recover energy from high Urea reactor has been revamped by operation to minimize energy consumptionpressure process gas in a recent revamp. almost all units by replacement of old trays and / or maximize production. The result There have also been some process with hydro-dynamically more efficient of recent energy conservation efforts aremodifications in the synthesis loop. trays. This measure improved conversion shown in Table 3.Installation of S-50 converter with MP in the reactor. Installation of vacuum pre- Table 3 – Result of recent energywaste heat boiler is reported to have given concentrator and pre-decomposer helped conservation effortsenergy saving of the order of 0.13 GCal/ Company Savings GCal/MT Percentage to reduce energy consumption andMT. Additional converter has increased of ammonia improvement improve product quality in a number ofconversion from 14% to 19% resulting in (%) units. Installation of pre-concentratorsaving in recycle energy. Similarly one of A 0.837 9 reduced the heat load on the first stage B 2.26 > 20 evaporator resulting in steam saving. Pre-the units has installed S-300 converter C 0.255 >3with energy saving of 0.34 GCal/MT. decomposer reduced the load of stripper INDIAN JOURNAL OF FERTILISERS December 2008 19
  4. 4. and MP/LP sections improving reliability 9.5of these equipments. In one of the unitscommissioned in 1984-85, a saving of 120 9.0 8.87kg/MT urea was realised in all the four Energy (GCal/MT) 8.5streams. In a 1981 plant, 200 kg LP steam/MT was saved with installation of pre- 8.0concentrator. In the same plant 7.5replacement of urea old stripper with newbimetallic stripper resulted in saving of 7.00.05 MT steam/MT. In yet another unit of 6.51984 vintage, vacuum pre-concentrator, 6.29MP pre-decomposer, additional trays in 6.0urea reactor, steam booster ejector for 1* 8 1 2 3 4 5 6 7 8 9 0 2 3 4 5 6 7 8 -8 -9 -9 -9 -9 -9 -9 -9 -9 -9 -0 -0 -0 -0 -0 -0 -0 -0 -0 87 90 91 92 93 94 95 96 97 98 99 01 02 03 04 05 06 07 00 19 19 19 19 19 19 19 19 19 19 19 20 20 20 20 20 20 20utilisation of surplus LP steam in MP 20decomposer and new bimetallic stripper Yearsaved 120 kg/MT of steam. Figure 2 – Energy consumption trends in urea plants Carbon dioxide compressor is majorenergy consumer in urea plants. The weighted average energy capacity. New projects would be based onRefurbishing the compressor with better consumption of the urea plants in the the most efficient process impellers and change of motor has country for the year 2007-08 is given in Further, fuel oil based plants accounts forimproved the efficiency of compressors. Table 5. The best plant achieved energy about 10% ammonia production capacity.Similarly revamp / refurbishing of turbines consumption of 5.16 GCal/MT urea for the These plants are expected to convert tohelped to reduce the consumption of year 2007-08. Figure 2 shows the trend gas in near future. This will improve thesteam. A few units have replaced the in energy consumption of urea plants energy efficiency of these plantsturbine and / or compressor for large reflecting about 30% improvement in significantlyenergy savings and improvement in energy over a 20-year period. 6.0 CONCLUSIONreliability. Table 5 – Feedstock-wise energy AMMONIA AND UREA INDUSTRY HAS COME Change of cooling tower fans, consumption of urea plants a long way in terms of capacity expansionreplacement of insulation, steam trap Feedstock Production Energy and improvement in energy efficiency. (MMT) consumption Modernization of old plants andmanagement, etc. have helped to save (GCal/MT)energy. A number of units have modified installation of new plants with better Gas 16.12 5.97internals of pumps (e.g. trimming of feedstock and technology have helped to Naphtha 1.60 7.17impeller) to match the load and reduce the Fuel Oil 2.17 7.99 reduce the energy intensity of the industry.steam / power consumption. Installation of Overall 19.89 6.29 The energy consumption was reducedmore efficient impellers also reduced the from 12.48 GCal/MT in 1987-88 to 8.97steam consumption. For smaller duty 5.0 FUTURE DEVELOPMENTS GCal/MT in 2007-08 for ammonia plants.pumps (1 MW) motor drives are more THE PLANTS WOULD CONTINUE TO CARRY For the same period the energyefficient than steam drives. Wherever, out the measures to improve their consumption of urea plants came downthere are both types of drives (including efficiencies. Revamp and retrofit measures from 8.87 GCal/MT (1987-88) to 6.29 GCal/stand by), mere operational changes has are under implementation in a number of MT (2007-08). Revamp and retrofitsaved energy. Elsewhere, even units. According to an estimate the projects are under way in a number ofreplacement of drives has been found to demand for urea production is expected to units. This alongwith conversion of non-be an attractive measure. There has been reach 28.8 million tonnes by 2011-12 i.e. a gas plants to gas would help to furtheremphasis in recent years to save energy short fall of about 2.8 million tonnes from increase the efficiency of this energyin various pumps by way of modification the 2007-08 production level. Part of the intensive segment of the fertiliser sector.of pumps to improve efficiency to optimize demand would be met by de-bottlenecking REFERENCEStheir operation to reduce energy the present capacities and the rest to be 1. S. Nand & V. Sood, “Energy Conservation Efforts in Indian Ammonia and Urea Plants”,consumption. Changes in operational met by expansion and greenfield projects. Proceedings of the FAI Workshop on Energyphilosophy and minor changes in The de-bottlenecking projects are Conservation and Management in Fertiliserhardware are also helpful. One of the expected to be bundled with energy Industry, 3-4 March, 2003, New Delhi.units has installed a small booster cooling efficiency schemes. One of the companies 2. S. Nand & Manish Goswami, “Energywater pump and now run only 3 regular has already implemented the energy Efficiency Gains in Indian Ammonia Plants: Retrospect and Prospect”, IFA Technicalpumps along with a booster pump instead saving schemes in all its units to improve Symposium, 25-28 April, 2006, Vilnius,of running 4 regular pumps. energy efficiency as well as increase in Lithuania.20 INDIAN JOURNAL OF FERTILISERS December 2008