M. Siddhartha Bhatt

Energy audit case studies I - steam systems

This paper presents an analytical diagnostic tool for energy audit of steam systems. The circuit efficiency is determined as a product of the segment efficiencies. The analysis is applied to a few industrial cases. These will provide clear indication on the pattern of energy losses and will aid in decision support for evolution of energy conservation measures. The results indicate that contrary to the popular thrust areas, the steam lines and the condensate loss are the major causes of fuel energy wastage and these offer considerable potential for conservation.

Mapping of general combined heat and power systems

Abstract In a combined heat and power (CHP) plant, the heating and electrical loads are mutually exclusive and cannot be chosen independent of each other. This paper reports on the mapping of the ranges of the heat-to-power ratios (HPRs) for given fractions of the electrical output. Alternatives for matching the HPRs of the CHP plant (source) and target process (load) are also discussed. It is shown that the maximum overall efficiency of CHP plants is about 90%. Design equations for the overall efficiency and HPRs of Diesel generating sets, boiler–steam turbine–generator units and combined cycle plants have been provided as a function of the fraction of the electrical output for optimal and rational design of the systems.

Performance enhancement in coal fired thermal power plants. Part IV : Overall system

This paper provides an analysis of the overall performance of 22 coal-fired power plants. The net overall efficiency is in the range 19·23–30·69%. The effects of ash in coal, contaminants in feed water, leakage, incondensables, etc., have been quantified. Ways of minimizing secondary oil consumption have been provided. The techniques for performance improvement, low cost as well as capital intensive, have been described. The role of overhauling the plant and associated opportunities for performance improvement are also discussed. It is concluded that achieving a high annual plant load factor (PLF) will bring about all round improvement in the unit performance. Unless the pressing problems of high ash in coal, inadequate contaminant control and leakage/ingress are solved, mere repowering by equipment of higher efficiency may not yield the desired results. Design margins of 10–20% are essential for both repowered and new units. In the long term, it is economical to de-commission all units below 210 MW and only three sizes need be retained: 210, 500 and 1000 MW. Automation of the DM water plant provides maximum economic advantage. Considerable opportunity exists for energy conservation through introduction of information technology and variable frequency drives in all units. Copyright

Effect of Ash in Coal on the Performance of Coal Fired Thermal Power Plants. Part I: Primary Energy Effects

This article reports the effect of ash content in raw coal on the energy performance of coal fired thermal power plants of capacity range 30–500 MW. The focus is on primary energy effects—combustion, heat transfer, and flow hydrodynamics. The effects of variation of ash in coal from 6% (taken as standard) up to 75% on component performance are studied and overall unit performance is quantified based on experimental data. When the ash content increases from 6% to 75%, the effects on the system (without fuel oil support) are as follows: (a) total boiler area requirement (excluding air preheater [APH]) increases by 69%, (b) efficiency of boiler fans drop by 22%–27%, (c) drum mills show an increase in SEC of 115% while ball-race mills and bowl mills show an increase in SEC of 30%, (d) induced draft (ID), forced draft (FD), and primary air (PA) fans show an increase in specific energy consumption (SEC) of around 30%, 6%–14%, and 2%–7% respectively, (e) the gross and net overall efficiencies are reduced to 77% and 66% of their original values, (f) the ratio of the specific fuel consumption at a given ash content to that at standard ash of 6% increases from 1 to 10, and (g) specific fuel consumption (SFC) gross increases from 0.35 to 3.0. When the ash content of coal goes beyond 57%, limitations in combustion space and flow arise, and beyond this the unit has to be operated only at partial load. When the ash in coal exceeds 75%, its UHV is reduced to zero.

Performance enhancement in coal fired thermal power plants. Part II: steam turbines

This paper presents the results of the performance enhancement study on 22 coal fired thermal power stations of capacities 30–500 MW. The oldest units (30 MW) have served for 33yr and the newer units (500 MW) have been in operation since 7yr. The turbine efficiencies are in the range 31·00–41·90% as compared to the design range of 34·80–43·97%. The isentropic efficiencies are in the range 74·13–86·40% as compared to design values of 83·20–89·10%. Considerable scope for efficiency improvement through low cost solutions: operational optimization, capital overhaul, simple modifications, etc., exists for all classes of units. The efficiencies can be restored to their design values. The developments in turbines over the last quarter of this century which have led to improved isentropic and thermal efficiencies must be adopted for existing units through retrofits, upgrades and revamps. The turbine efficiencies can be improved to 38·0% for 30 MW units and to 47% for 500 MW units. The maximum potential is for improvement in 210 and 500 MW units followed by 110 and 120 MW units. The potential for 30 and 62·5 MW units is rather limited because of their low capacity share, lack of interest in manufacturers to sell spares (because of the low volume of requirement) and large pay back periods for modernisation schemes. Copyright

Generalized neural network methodology for short term solar power forecasting

The main objective of this paper is to perform data analysis of ground based measurement and review the state of the art of IIT Jodhpur Rooftop solar photovoltaic installed 101 kW system. Solar power forecasting is playing a key role in solar PV park installation, operation and accurate solar power dispatchability as well as scheduling. Solar Power varies with time and geographical locations and meteorological conditions such as ambient temperature, wind velocity, solar radiation and module temperature. The location of Solar PV system is the main reason of solar power variability. Solar variability totally depends on system losses (deterministic losses) and weather parameter (stochastic losses). In the case of solar power, deterministic losses can be found out accurately but stochastic losses are very uncertain and unpredicted in nature. The proposed soft computing technique will be suitable for solar power forecasting modeling. In this paper Fuzzy theory, Adaptive Neuro-fuzzy interface system, artificial neural network and generalized neural network are used as powerful tool of solar power Forecasting. This soft computing cum nature inspired techniques are able to accurately and fast forecasting compared to conventional methods of forecasting. This is done analyzing the operational data of 101 kW PV systems (43.30 kW located in Block 1 and 58.08 kW in Block 2), during the year 2011.

Performance enhancement in coal-fired thermal power plants. Part III: auxiliary power

Auxiliary power in coal-fired power stations accounts for 7% (500 MW units) to 12% (30 MW units) of the gross generated power at the full plant load. The minimum AP varies between 4·5 and 9·0% for the same capacity range. The excessive power due to factors such as coal quality, excessive steam flow, internal leakage/ingress in equipment, inefficient drives, distribution network losses, reduced power quality, ageing, etc., is quantified. An experimental study has shown that 85·7% of the AP in excess of the design value can be traced to coal quality and its indirect effects. The AP can be minimized even below the design value by operational optimization, overhaul of equipment and revamping. The paper discusses in detail the techniques for restoration of the AP to the designed value and further improvements. Copyright

Enhancing energy generation by use of efficient control for hybrid energy systems

This paper presents the design of control strategies, their effectiveness and energy enhancement potential for solar/wind/diesel integrated energy systems, solar thermal-biomass air heaters and solar thermal heat-pump hybrid water heaters. Use of control systems for optimising the usage of renewable energy sources with conventional energy systems is discussed.

Effect of Ash in Coal on the Performance of Coal Fired Thermal Power Plants. Part II: Capacity and Secondary Energy Effects

This article reports the secondary energy effects (wear/erosion/abrasion, slagging, and fouling) of ash in coal on the energy performance of coal fired thermal power plants of capacity range 30–500 MW. It also gives the extent of capacity reduction in equipment due to firing of coals with higher ash contents. At an ash content of 75% in coal, the effects on the system (without fuel oil support) follow: (a) decrease in Hardgrove index from 80 to 44; (b) 20% of the specific energy consumption (SEC) of induced draft (ID) fans, 10%–12% of that of forced draft (FD) and primary air (PA) fans, 17% of that of drum mills, and 12%–13% of that of ball-race mills and bowl mills, are accounted for by wear/erosion/abrasion effects; (c) decrease of fan efficiencies by 5%–6% points due to wear/erosion/abrasion effects; (d) capacity loss originating from wear/erosion/abrasion effects alone is 8% due to ID fans, 1% due to PA fans, and 6% due to mills; (e) fouling effects are high fouling factor, decrease in boiler efficiency by 3%, and capacity reduction of 2%; and (f) CFs based on overall unit performance are 31% for units below 210 MW, 26% for 210 MW units, and 40% for 500 MW. Considering the capacity restrictions due to individual equipment, CF at an ash content of 57% is 85% due to the boiler fans, 84% due to Raymond bowl mills and drum type ball mills, 71% due to slow speed large ball and race mills, and 88% due to ash slurry pumps. When the coal exceeds 70% and tends toward 76%, the heating value of coal tends toward zero. The effects of slagging (independent of ash content in coal) area 20% decrease in boiler water wall loading, a 3.5% points decrease in boiler efficiency, and capacity reduction of 14%.

Energy audit case studies II—air conditioning (cooling) systems

This paper discusses a novel methodology for determination of the efficiencies of each segment in a centralized air conditioning (A/C) plant. The methodology is useful analytical tool in energy audit where it can be used for decision support for evolution of energy conservation measures and techno-economic evaluation of the various options. The procedure is applied to three A/C plants of capacity range from 50 to 500 TR. Losses in chilled air ducts and cycling losses in the refrigerant circuit are identified to be the major causes for decrease in the efficiency and capacity under rating of the systems. Effective controls and insulation of air ducts: have been shown to be the most cost effective solutions to improve the energy efficiency of the A/C plants. The generalized experimental data on overall performance of sixteen A/C plants is also provided.