Feature

Energy Conservation - Critical to Reduce Cost of Operation

Posted on 21 January, 2010 | Tags: Energy Management

Rising energy cost is a major concern for the chemical industries, as this forms a major part of company's operational expenses. However, meticulous approach and proper planning can result in significant reduction in energy cost. GSFC has initiated and implemented various steps towards energy conservation to manage the energy cost in their industrial units, which have been discussed in this paper.

Since inception of Gujarat State Fertilizers and Chemicals Limited (GSFC), mammoth importance is given to Energy Conservation and is considered a vital tool to reduce cost of operation and thus enhance profit margin. In recent era, it has also assumed a newer and better role, ie, to retard rate of global warming by reducing fuel consumption hence reducing emission of Green House Gases (GHG). Obsolete technology, lower capacity utilization, casual metering and monitoring standards, lower automation, poor raw material quality and poor handling, operating and maintenance activities etc are the major reasons identified for higher energy consumption at GSFC. To increase efficiency of energy consuming operation by overcoming the reasons mentioned, GSFC puts up relentless effort.

Energy Conservation an Imperative
It has been experienced that at GSFC, cost of energy consumption amounts from 5-40 percent of total cost of production, which depends on the type of product, technology, production capacity, automation, stream days etc. In this era of competition, the margin available with the producer to reduce the cost of operation thereby increases the profit margin. Energy conservation has always been an imperative at GSFC. Energy conservation has been achieved at GSFC through various ways viz integration of two or more nos. of plants in which various products are supplied besides utilities, to reduce power and fuel consumption. Incorporation of new technologies like Vapor Absorption Heat Pump (utilizing waste low pressure steam) and Thermo Compressor System (recovering low pressure steam) is considered to reduce power and steam consumption respectively. Power consumption in Compressor System is reduced by adopting measures like avoiding excessive pressure drop in discharge loop, reduction in compressor inlet mass, incorporation of inter stage cooler, cooling compressor inlet gas, maintaining proper Cooling Water (CW) velocity in coolers etc. Attention is given to utilize turbine instead of throttling steam across control valve.
Turbine can be helpful either in reducing import of power or lessen fuel consumption to generate power by running machinery with less or no power consumption. To generate more power in back pressure turbine, more extraction of low-pressure steam in place of high-pressure steam is carried out. Vast use of waste heat streams to heat various process streams is adopted to reduce energy consumption. Based on pinch analysis, source of heat energy that is rejected to either cooling water system or used inefficiently is identified to heat up various process streams to reduce steam consumption. Use of low-pressure steam, which is generally vented, is used to preheat process streams to reduce consumption of high-pressure steam. Generation of high-pressure steam by flashing condensate, isolating idle steam headers, desuperheating, proper steam trap system, etc are different ways through which either steam generation is increased or steam consumption is reduced.
Power saving in pumping system is achieved by installing optimum capacity pump or by modifying system to avoid pumping requirement itself. Very often, adoption of simple ways such as, trimming of impeller, installation of low capacity motor, use of low pressure drop NRV, installation of high efficiency pumps etc. have been carried out to reduce power consumption. Use of FRP blades in place of Aluminum blades and recently hollow FRP blades in place of FRP blades is carried out in various cooling towers of GSFC. Use of magnetic amplifier, CDL in place of conventional tube lights etc is carried out widely at GSFC. To exploit the potential of renewable energy, GSFC has installed Wind farms and solar heaters have been installed by GSFC.
Energy is derived primarily from the non-renewable energy sources. Depletion of these resources will result in day-to-day increase in energy costs. Graph 1 represents the increase in power cost, steam and NG over a period of 3 years at GSFC.
GSFC is focused on energy conservation, which is the quickest and cheapest and most practical method to reduce cost of operation to maintain profit margin intact in the long-term business. At GSFC, energy is believed to be a manageable expense that can be controlled with dedicated efforts.

Array of Schemes to Curb Energy Costs
 Innumerable energy conservation schemes have already been implemented successfully at GSFC in the recent past. Various energy conservation measures implemented already are those under active consideration have been classified broadly under various categories are presented here.

1. Energy Conservation through Integration of Plants

• Supply of Vapor Ammonia from Ammonia-IV Plant to DAP Plant:
  Vapor ammonia generated in Ammonia-IV (A-IV) plant is liquefied in refrigeration system by running screw compressors, which consume power. Vapor ammonia is generated at Di-Ammonium Phosphate (DAP) plant by evaporation of liquid ammonia, by consuming steam.  Scheme implemented to export vapour ammonia from A-IV to DAP plant. It reduced loading of vapour ammonia on refrigeration compressor by ~2.5 MT/Hr. It resulted into power saving at A-IV plant by 8.0 lakhs unit/Yr (Rs 16 lakhs/Yr) and steam saving at DAP plant. Cost of modification is Rs. 30.68 lakhs. Payback period is lesser than 3 years.

2. Incorporation of New Technologies

• Use of Vapor Absorption Heat Pump (VAHP) at Caprolactam-2 plant.
  Chilled water, used for process cooling, was cooled down from ~100C to ~70C by Freon-22 based compressor refrigeration system. Since low pressure steam is in excess, a lithium bromide based VAHP is provided.  It has become possible to cool down chilled water through VAHP and use of refrigeration compressor is totally eliminated. It resulted into power saving by 18.96 lacs unit/Year (Rs 38 lakhs/Year). Cost of modification is Rs. 80 lacs. Payback period is about 2 years.
• Installation of Thermo Compressor System (TCS) at Caprolactam-2 plant.
  Use of steam of different pressures is carried out in plant, to the possible extent, and then finally very Low Pressure Steam (LPS) is either vented or condensed, and in both the ways, energy is lost. LPS can be reutilized fruitfully, instead of venting or condensing, by elevating its pressure by utilizing High Pressure Steam (HPS) as driving force. In a special device called TCS, HPS acts as motive fluid and it is passed through specially designed nozzle. Due to ejector like system, LPS gets sucked and final outcome is Medium Pressure Steam (MPS), which can be fruitfully reused.  Installation of TCS is under planning.  Requirement of HPS depends upon some factors like quantity of LPS, pressure of LPS and HPS, final pressure of MPS required, quantity of MPS generated etc. Anticipated steam recovery is ~16000 MTPY (Rs 90 lakhs/Year) which can be effectively utilized. Cost of modification is Rs 30 lakhs. Anticipated payback period is < 6 months.

3. Improvement in Compressor System

• Reduction in Discharge Pressure of Centrifugal Compressors:
  At Ammonia-IV plant, pure H2 and pure N2 are mixed to form synthesis gas for further processing in ammonia synthesis section. It was observed that pressure of N2 loop had to be kept about 2 bar more than H2 loop pressure. Cause of high pressure drop, ie N2 Flow Control Valve (FCV) in N2 compressor discharge loop was identified. Bypass valve to FCV was provided and some quantity of N¬2 was allowed to pass through it. It resulted in to less pressure drop across FCV. To that extent, N2 compressor discharge pressure could be reduced, being a centrifugal compressor. It resulted in to less power consumption by ~13.7 lacs unit/Year (Rs 27 lakhs/Year). Cost of modification is Rs 0.7 lakhs. Payback period is of few days.
• Reduction in Compressor Inlet Mass:
  Reduction in vapour quantity to be handled by compressor can result in to power saving.  Liquid ammonia is supplied to chill the circulating mass in Hydroxylamine sulphate (HX) section of Caprolactam-1 (Cap-1) plant. Generated vapor ammonia is supplied to reciprocating refrigeration compressor. In Lactam section of Cap-1 plant, 24% ammonia solution is used, which is prepared by mixing liquid ammonia and DMW. Scheme prepared to absorb vapor ammonia generated in HX plant in absorber with definite quantity of DMW so as to prepare 24% ammonia solution. Due to reduction in vapor loading on reciprocating ammonia refrigeration compressor by ~3 MT/Hr, loading on compressor could be reduced from 100% to 75%, resulting in to substantial power saving.

4. Power Generation through Turbine

• Avoidance of Steam Throttling:
  Care should be taken to expand the steam across the turbine in place of throttling as latter is a waste of energy. Steam of 37 barg pressure is imported at Caprolactam-2 plant and throttled across pressure reduction stations to different pressure level ie, 20 barg and 14 barg, as per the requirement. Scheme is prepared to install a turbine to expand 37 barg steam to 20 and 14 barg respectively. Expected power generation is ~104 lacs units/Yr (Rs 208 lakhs/Yr). Anticipated payback period is < 6 months.

5. Utilization of Waste Steam for Heating
Through pinch analysis, source of heat energy being rejected to either cooling water system or used in inefficient way can be utilized to heat up various process streams to reduce steam consumption.

• Installation of Anol Feed pre heater:
  Gases coming out of Dehydrogenation section of Caprolactam-1 plant was cooled down from ~2200C to ~1500C by utilizing cooling water (CW) Feed to section was supplied at ~500C from storage tank to Anol evaporator and heated up to boiling point of mixture, ie ~1750C corresponding to operating condition, by utilizing 37 barg steam. As temperature of tube skin in Anol evaporator was reaching up to ~2000C, Cyclohexanol was getting decomposed to heavy acids, resulting in to corrosion and finally in to tube leakages. Scheme prepared to install a heat exchanger to preheat feed to Dehydrogenation section from ~500C to 850C by utilizing heat content of gases coming out of reactor (~2200C) and rejecting heat to cooling water system. Above mentioned system resulted in to less steam consumption by ~200 kg/Hr in Anol evaporator. Subsequently it reduced steam side pressure and hence, mean metal temperature reduced below 2000C. Corrosion rate reduced and evaporator is giving much longer operating life. Steam saving of 1600 MTPY (Rs 9.0 lakhs/Yr) realized. Cost of modification is Rs 5 lakhs. Payback period is less than 6 months.
• If low-pressure steam (LPS) is in excess and being vented or condensed, it is better to consume LPS to heat up the process stream to reduce high pressure steam consumption.
  Heating up of Soda solution at Caprolactam-2 plant:
  At Caprolactam-2 plant, it was observed that LPS (2.5 barg) is in excess. Soda solution supplied to neutralize acids and saponify esters, is heated up from ~500C to ~1500C by utilizing 10 barg steam. Scheme initiated to install a preheater to elevate temperature of soda solution from ~500C to ~1300C by utilizing LPS as heating media. Further heating up to ~1500C will be carried out in Soda solution heater by utilizing 10 barg steam as per normal practice. Anticipated saving of 10 barg steam is 3440 MTPY (Rs 19.2 lakhs/Year). Anticipated Payback period is less than one year.

6. Power Saving in Pumping System 
Several different types of pumps are used at GSFC. Pumps are one of the major power consuming machineries. Hence, at GSFC, special attention is given depending upon its use, capacity, type and operating efficiency level, etc to reduce power consumption by adopting following methods.

• Optimization of Pumping System: Power consumption can be reduced by either installing optimum capacity pump or by modifying system to avoid pumping requirement itself. Following schemes have been implemented at GSFC based on optimization.

1) Using common CW pump for CoGen-I/II & CoGen-III plant:
At CoGen-III plant, two nos. of pumps were provided with different capacities, ie CWP of 1000 m3/Hr, supplying CW partly to Gas turbine (GTG) and partly to Steam turbine (STG-III) and CCWP of 6000 m3/Hr exclusively for STG-III to bear condensing load. Based on steam and power balance of entire complex, STG-III is not running. It resulted in to complete stoppage of CCWP and created margin of ~500 m3/Hr in CWP.
Another CW pump of ~400 m3/Hr capacity was running to meet the requirement of CoGen-I & II. Looking to the margin available in CWP associated with CoGen-III; C.W. diverted from CoGen-III plant to CoGen-I/II plant by utilizing interconnection, already available. It became possible to stop CW pump (~400 m3/Hr) associated with CoGen-I/II plant. It resulted in to power saving by 5.1 lakhs units/Year, (Rs 11.5 lakhs/Year). Cost of modification is nil as existing system was optimized.

2) Installation of optimum size pump:
CoGen-III plant is equipped with Gas turbine (GTG) and Steam turbine (STG-III). Steam of 37 barg pressure is generated in Heat Recovery and Steam Generation (HRSG) unit of Gas turbine, by utilizing heat of flue gases coming out of GTG. Provision is available to feed natural gas (NG) in the duct of HRSG to produce additional steam. Generated steam is supplied to STG-III to produce power. Requirement of boiler feed water is fulfilled by operating Make up water pump (MUPW pump), which supplies fresh DMW to deaerator. STG-III is not running based on steam and power balance and hence, additional steam is not produced in HRSG duct. Revised methodology of operation created big margin in MUPW pump and it was operating at low capacity and hence at low efficiency. Scheme prepared to install low capacity, low head and high efficiency MUPW pump. Such modification resulted in to power saving of by 1.6 lakhs units/Year, (Rs  3.2 lakhs/Year). Cost of modification is Rs 3 lakhs. Achieved payback period is about one year.

3) Alternate to  pumping system:
In Nylon-6 plant, steam is condensed in barometric condensers, located at 12 meter elevation, with direct contact of CW. Thus generated mixture of CW and condensate was supplied to holding vessel, located at ground level and then it was pumped by condensate transfer pump to Cooling Tower (CT). Operation of subject pump was based on level in holding vessel, ie on sensing high level, pump will get start and on sensing low level, it will get stopped. Due to low capacity of holding vessel, frequency of subject pump getting on and off was very high. It resulted in to high maintenance cost. Scheme prepared to install a direct header to supply mixture of CW and condensate by gravity to the basin of CT. It resulted in to stoppage of pump and power saving by 0.5 lacs units/Year, (Rs 1.12 lakhs/Year) besides saving on maintenance cost. Cost of modification is Rs 3.25 lakhs. Payback period is about three years.

• Trimming of impeller and installation of low rating electric motor:
  Trimming is simple, cheap but yet effective manner of reducing power consumption in pumps. Depending upon the margin available, revised impeller dia can be worked out. At Ammonia-IV plant, entire liquid ammonia production (~56 MT/Hr) is supplied to Ammonia storage tank at -33 0C by operating ammonia product pump. Provision is available to supply liquid ammonia directly at ~0 0C and ~17 barg pressure from A-IV plant to various users. As a result of which, loading on subject pump got reduced. Based on margin available, impeller trimming carried out. Power consumption got reduced by 0.56 lacs units/Year (Rs 1.26 lakhs/Year). Cost of modification is 0.05 lacs and payback period < 10 days. As actual power consumption value was much less i.e. ~20 kWh and motor installed was of ~42 kW rating, new motor of lower rating (23 kW) was installed at later stage. It resulted into further power conservation by ~2.5 kWh on account of reduction in no load current drawn by motor.
• Installation of High Efficiency Pumps:
  Operation of pump at lower efficiency level results in to undue additional power consumption.  In Caprolactam-1 plant, CW pumps were operated at very low efficiency, ie ~55 percent. New pumps having higher capacity, higher head and high efficiency (~80 percent) were installed. Power consumption value per m3 circulation got reduced from 0.169 to 0.146 kWh/m3.

7. Steam Saving Measures

• Generation of High Pressure Flash Steam:
  At Ammonia-IV plant, blow down of condensate is carried out from 105 barg steam system. Condensate is supplied to Low pressure Flash drum operated at 5 barg pressure. Steam generated at 5 barg pressure due to flashing is supplied to Turbo Generator (TG) to produce power. Based on steam and power balance, TG is not functional and at present 5 barg steam produced is vented, as it is in excess.  Scheme is prepared to produce 37 barg flash steam by supplying condensate to a medium pressure Flash drum. Rest of the flashing is to be carried out in low pressure flash drum as per normal practice. Such operation will produce additional 37 barg steam by 6400 MTPY (Rs 36 lakhs/Year) which can be effectively utilized within plant or can be exported to the GSFC grid. Cost of modification is Rs 11.5 lacs. Anticipated payback period is lesser than 6 months.
• Isolating Idle Steam Headers:
  At Ammonia-IV plant, Natural gas (NG) and Naphtha (NA) can be utilized in any proportion either as feed or fuel or as both so as to run plant at required capacity. At later stage, due to availability of NG, use of naphtha was stopped. However, 37 barg steam supply to NA section remained live although NA handling sections were not operated. Steam loss was taking place through leakages from various locations like, NA turbine, NA reboiler, steam trap network, steam FT, service station, and steam flow control valve besides loss due to condensation as a result of heat loss though insulation. During annual shutdown, spare isolation valve was provided to isolate steam header to curb steam losses. It resulted in to steam saving by 640 MTPY (Rs 3.6 lakhs/Year). Payback period is of few days.  
• Energy saving by using Energy efficient lighting sources.
  During year 2008-09, installation of energy efficient lighting is carried out as mentioned below
• 40 Nos. 400 W HPMV fittings replaced by 15 NOs. of 150 W Metal halide lighting fittings at Urea plant saving 1.205 Lakhs units/ year. 
• Installation of magnetic amplifier panel to reduce power consumption of lighting at SA-IV plant saving 0.372 Lakhs units/ year. 
• 11850 Nos. 40 W tube lights with electromagnetic choke replaced by 28 W T5 fittings with electronic ballast saving 17.847 lakhs units/ Year.
• Magnetic amplifier type lighting energy saver installed at 13 number of various locations with guaranteed power saving of about 15 percent wr to existing gas discharge lamps. Anticipated annual saving on lighting energy is of 2.36 lakhs units/Year.

Above mentioned measures resulted in to aggregate annual saving at a rate of 21.78 lakhs units (Rs 44.0 lakhs). Energy conservation becomes our joint responsibility, be it the industries, individual citizens, organizations, oil companies, or the government. Each one of us has a specific and significant role to play.

- Article Courtesy: GSFC Ltd