Rangan Banerjee

Energy balance and cogeneration for a cement plant

The cement industry is an energy intensive industry consuming about 4 GJ per tonne of cement produced. A thermodynamic analysis for cogeneration using the waste heat streams is not easily available. Data from a working 1 Mt per annum plant in India is used to obtain an energy balance for the system and a Sankey diagram is drawn. It is found that about 35% of the input energy is being lost with the waste heat streams. A steam cycle is selected to recover the heat from the streams using a waste heat recovery steam generator and it is estimated that about 4.4 MW of electricity can be generated. This represents about 30% of the electricity requirement of the plant and a 10% improvement in the primary energy efficiency of the plant. The payback period for the system is found to be within two years.

Optimal operation of industrial cogeneration for load management

This paper presents a generalized formulation to determine the optimal operating strategy of industrial cogeneration schemes. The model includes both electrical and thermal systems. All types of cogeneration equipment viz steam turbines, gas turbines, diesel generators, steam boilers, waste heat recovery boilers, and steam header configuration, with grid connection are separately represented in terms of their characteristics so that the model has the flexibility to be applicable for any industry. The model is multiperiod and nonlinear in nature and utilizes a Newton based algorithm for minimizing the total operating cost. Optimal operating strategies for different equipment combinations for a typical industrial configuration under different electricity tariff rates are determined using the proposed model. The results show that industrial cogeneration has a significant potential in reducing peak coincident demand. The optimal response of cogeneration plant reduces the peak coincident demand by 42.8 MW (71%) under flat tariff and 54 MW (90%) under TOU tariff. The industry gets 16% saving in the total operating cost with the optimal operation of the cogeneration plant. When power export is permitted to grid, it provides the utility a peak saving of 63.7 MW.

Load-management applications for the industrial sector

The goal of any load-management program is to maintain, as nearly as possible, a constant level of load, thereby allowing the system load factor to approach 100%. The important benefits of load management are reduction in maximum demand, reduction in power loss, better equipment utilisation and saving through reduced maximum demand charges. Load shifting, one of the simplest methods of load management, is to reduce customer demand during the peak period by shifting the use of appliances and equipment to partial peak and off-peak periods. Here no loads are being switched off, but only shifted or rescheduled, and hence the total production is not affected. In this paper, a fully fledged program is developed for load shifting and the same has been tried with the actual load data collected from a typical fertiliser and chemical industry plant.

New methodology for estimating biofuel consumption for cooking: Atmospheric emissions of black carbon and sulfur dioxide from India

[1] The dominance of biofuel combustion emissions in the Indian region, and the inherently large uncertainty in biofuel use estimates based on cooking energy surveys, prompted the current work, which develops a new methodology for estimating biofuel consumption for cooking. This is based on food consumption statistics, and the specific energy for food cooking. Estimated biofuel consumption in India was 379 (247– 584) Tg yr � 1 . New information on the user population of different biofuels was compiled at a state level, to derive the biofuel mix, which varied regionally and was 74:16:10%, respectively, of fuelwood, dung cake and crop waste, at a national level. Importantly, the uncertainty in biofuel use from quantitative error assessment using the new methodology is around 50%, giving a narrower bound than in previous works. From this new activity data and currently used black carbon emission factors, the black carbon (BC) emissions from biofuel combustion were estimated as 220 (65–760) Gg yr � 1 . The largest BC emissions were from fuelwood (75%), with lower contributions from dung cake (16%) and crop waste (9%). The uncertainty of 245% in the BC emissions estimate is now governed by the large spread in BC emission factors from biofuel combustion (122%), implying the need for reducing this uncertainty through measurements. Emission factors of SO2 from combustion of biofuels widely used in India were measured, and ranged 0.03–0.08 g kg � 1 from combustion of two wood species, 0.05–0.20 g kg � 1 from 10 crop waste types, and 0.88 g kg � 1 from dung cake, significantly lower than currently used emission factors for wood and crop waste. Estimated SO2 emissions from biofuels of 75 (36–160) Gg yr � 1 were about a factor of 3 lower than that in recent studies, with a large contribution from dung cake (73%), followed by fuelwood (21%) and crop waste (6%). INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; KEYWORDS: aerosols, emission inventory, regional pollution

Energy and cogeneration targeting for a sugar factory

The sugar industry in India has a potential of 3500 MW to export to the grid. In this paper an energy balance has been carried out for an actual 5000 TCD plant and a Sankey diagram is drawn. A pinch analysis is done for the sugar factory and reveals that the minimum hot utility requirement is lower than the actual by 9%. Modified evaporator designs are proposed as it has been found that the existing plant is not optimum with regard to the surface area of the evaporators and the amount of steam being consumed. Exergy analysis is applied to the existing and the proposed evaporator effects and the results are compared. It is concluded that the amount of steam consumption will reduce by 9 T/h and exergy losses are reduced by 48% of its original value if the existing quadruple effect is modified to a quintuple effect. The turbine hardware model is used to predict the optimum amount of power that can be cogenerated from the system for different generation temperatures at a pressure of 45 bar. The optimum superheat temperature is found to be 600 °C for a backpressure turbine with single extraction. A cost analysis is performed to determine the variation of the average cost of generation of power with the generation temperature of the steam.

Optimal cool storage capacity for load management

Cool storage is a load management strategy for air conditioning loads, which shifts peak load by storing cooling capacity during off peak period. It allows the customer’s electricity use for cooling to be shifted to off peak period, benefiting both the consumer and the utility. Reduction in peak demand and electricity cost depend on electricity tariff rates, operating strategy, cool storage capacity and climatic conditions. In this paper, a methodology is presented to determine the optimal chilled water storage (CWS) capacity and corresponding operating strategy for the air conditioning loads for different electricity tariffs. This model minimizes the total operating cost of the air conditioning plant by a trade-off between the cost involved for providing the storage and accessories and savings achieved under the specified electricity tariff. A case study for a typical office complex shows that a reduction of 38% in peak demand is possible by adopting the optimal CWS strategy under time of use (TOU) tariff. The corresponding saving in the operating cost for the consumer is 5.9%. The results show that under flat tariffs, the prevalent high consumer discount rates make cool storage unviable. This provides justification for utility intervention in cool storage demand side management (DSM) programs.

Sustainability analysis of renewables for climate change mitigation

Carbon dioxide is a major greenhouse gas (GHG) responsible for climate change. The energy sector accounts for approximately 75 % of the total carbon dioxide emissions in the world. The main options for reducing carbon dioxide emissions in energy systems are energy efficiency, and utilization of renewable energy and nuclear energy. In the present global energy scenario, the share of modern renewables in the total primary energy use is marginal (about 4.5 %). This paper assesses the sustainability of renewables for the world using the criteria of life-cycle cost, net energy ratio, resource constraint and greenhouse gas emissions. Renewable options for electricity generation and hydrogen generation for vehicles are assessed on the basis of these criteria. Life-cycle assessment (LCA) is carried out using SimaPro 6 LCA software. For electricity generation the base case considered is thermal power generation using coal. The options considered are wind energy, solar photovoltaics and biomass gasification. For hydrogen production three methods based on renewables (photovoltaic (PV)-electrolysis, wind energy conversion systems (WECS)-electrolysis and biomass gasification) are compared with the steam methane reforming (SMR) method. The renewable-based technologies seem to be sustainable on the basis of all criteria except the high life-cycle cost. In some cases, e.g., in biomass-based systems, land availability may constrain sustainability. Biomass is likely to be a sustainable solution only if marginal/scrub lands can be used for biomass plantation with adequate yield. However, this option needs to be studied to see if the net energy ratio is greater than one. It is found that hydrogen production by photovoltaic-electrolyzer can be a non-renewable method at low load factor (~0.15) and PV module efficiency (10 %). However, this method is renewable for higher values of load factor and PV module efficiency. The framework developed in this paper can form the starting-point for sustainability analysis.

Biomass pyrolysis for power generation -- a potential technology

A wide range of process and routes are available for power generation from biomass. PYROLYSIS is another emerging technology, wherein biomass is converted to liquids, gases and char — liquid fuels being the main target. Power generation using this technology is essentially the use of pyrolytic oils for the gas turbine integrated into a combined cycle. Using this process has an inherent advantage of potentially decoupling of the fuel-generation from the power- generation site. A comparative study of this technology for power generation, with other technologies is made to determine its economic viability. Despite the fact that this technology is relatively new in the learning curve, it is found comparable with the other routes studied. It is found that the biomass prices have a strong influence in the economics, and using pyrolysis for power generation would be a more favored route than others at higher biomass prices. The study clearly brings out power generation through pyrolysis as a potential route and deserves attention.

Sizing curve for design of isolated power systems

Isolated power systems meet electricity demand by generating power close to its point of utilisation. They are an option to electrify communities located in remote areas where extending the grid could be uneconomic. Diesel generators, photovoltaic panels and energy storage using battery banks have been used for meeting the electrification needs of remote areas. The design objective for such systems is the estimation of the ratings of the generators and the storage capacity requirements for meeting specified reliability and economic constraints. A review of different methods for sizing photovoltaic-battery systems indicates that they fall into mainly two categories, analytical methods and simulation-based schemes. A generalised methodology for generating a “sizing curve” relating the generator rating and storage capacity, based on a time series simulation approach, is presented in this paper. It helps in the identification of a “design space” which enables the exploration of all the feasible system configurations meeting a given demand for a site. It further serves as a tool for system optimisation. Two specific options for isolated power generation, diesel generator-battery system and photovoltaic-battery system, are illustrated for a typical Indian site. Sizing curve and design space are plotted on normalised generator rating vs. storage capacity coordinates for these options.

Exergy analysis of pressure swing adsorption processes for air separation

Pressure swing adsorption cycles for the production of oxygen from air have been analysed for equilibrium separations, using the method of exergy analysis. The optimum operating point has been determined and individual component losses identified. A modified cycle incorporating a pressure equalisation step has been found to be superior in terms of its power requirements. The methodology of exergy analysis provides a rational criterion for determination of the optimal operating parameters for a specified configuration and for comparing different configurations.