ENERGY EFFICIENCY IN THERMAL UTILITIES AND SYSTEM

Energy Efficiency It can be termed as the ratio of useful energy output to the total energy input. It’s denoted by Ƞ. Equipments are said to be efficient if they are utiliting maximum amount of input energy.

Boiler It’s defined as “a closed vessel in which or other liquid is heated, superheated steam under high pressure is generated for the purpose of generation of power from superheated steam”. They are classified water/fire tube boiler, operating pressure of boiler, operating position of boiler etc.

Energy Performance Assessment of Boiler Purpose of performance test To find out efficiency of boiler To find out evaporation ratio The purpose of performance test is to determine actual performance and efficiency of boiler and compare it with design values and norms.

Boiler efficiency, Ƞ= 𝐻𝑒𝑎𝑡 𝑜𝑢𝑡𝑝𝑢𝑡 𝐻𝑒𝑎𝑡 𝑖𝑛𝑝𝑢𝑡 ×100 Ƞ= 𝐻𝑒𝑎𝑡 𝑜𝑢𝑡𝑝𝑢𝑡 𝑖𝑛 𝑓𝑜𝑟𝑚 𝑜𝑓 𝑠𝑡𝑒𝑎𝑚 (𝑘𝐶𝑎𝑙𝑠) 𝐻𝑒𝑎𝑡 𝑖𝑛𝑝𝑢𝑡 𝑖𝑛 𝑓𝑜𝑟𝑚 𝑜𝑓 𝑓𝑢𝑒𝑙 (/𝑘𝐶𝑎𝑙𝑠) ×100 Evaporation ratio = 𝑄𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 ℎ𝑒𝑎𝑡 𝑔𝑒𝑛𝑒𝑟𝑎𝑡𝑒𝑑 𝑄𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑓𝑢𝑒𝑙 𝑐𝑜𝑛𝑠𝑢𝑚𝑝𝑡𝑖𝑜𝑛

Boiler efficiency can be tested by following method: Direct Method: Where the energy gain of working fluid (water and steam) is compared with energy content of boiler fuel. Indirect Method: Where the efficiency is the difference between losses and energy input.

Direct Method It is also known as “Input-Output Method” due to fact that it needs only the useful output (steam) and the heat input (i.e. fuel) for evaluating the efficiency. Boiler Efficiency= 𝐻𝑒𝑎𝑡 𝑂𝑢𝑡𝑝𝑢𝑡 𝐻𝑒𝑎𝑡 𝐼𝑛𝑝𝑢𝑡

Efficiency = 𝐻𝑒𝑎𝑡 𝑎𝑑𝑑𝑖𝑡𝑖𝑜𝑛 𝑡𝑜 𝑆𝑡𝑒𝑎𝑚 𝐺𝑟𝑜𝑠𝑠 𝐻𝑒𝑎𝑡 𝑖𝑛 𝐹𝑢𝑒𝑙 ×100 Boiler Efficiency= 𝑆𝑡𝑒𝑎𝑚 𝑓𝑙𝑜𝑤 ×(𝑠𝑡𝑒𝑎𝑚 𝑒𝑛𝑡ℎ𝑎𝑙𝑝𝑦 −𝑓𝑒𝑒𝑑 𝑤𝑎𝑡𝑒𝑟 𝑒𝑛𝑡ℎ𝑎𝑙𝑝𝑦) 𝐹𝑢𝑒𝑙 𝑓𝑖𝑟𝑖𝑛𝑔 𝑟𝑎𝑡𝑒 × 𝑔𝑟𝑜𝑠𝑠 𝑐𝑎𝑙𝑜𝑟𝑖𝑓𝑖𝑐 𝑣𝑎𝑙𝑢𝑒 ×100

Boiler efficiency = 𝑄 × 𝐻−ℎ ×100 (𝑞 ×𝐺𝐶𝑉) Where, Q =Quantity of steam generated per hour (kg/hr) q =Quantity of fuel used per hour (kg/hr) GCV=Gross calorific value of the fuel (kCal/kg) H =Enthalpy of steam (kCal/kg) h =Enthalpy of feed water (kCal/kg)

Merits & Demerits of Direct Method: Plant people can evaluate quickly the efficiency of boilers Requires few parameters for computation Needs few instruments for monitoring Demerits: Does not give clues to operate as to why efficiency of system is lower Does not calculate various losses accountable for various efficiency levels

Indirect Method The disadvantages of the direct method can be overcome by this method, which calculates the various heat losses associated with boiler. An important advantage of this method is that the error in measurement do not make significant change in efficiency. In indirect method, 1% error in measurement of losses will result in Efficiency = 100 – (10 ±0.1) 90 ± 0.1=89.9 𝑡𝑜 90.1

Losses Applicable to Liquid, Gas & Solid Fired Boiler L1. Loss due to dry flue gas (sensible heat) L2. Loss due to hydrogen in fuel (H2) L3. Loss due to moisture in fuel (H2O) L4. Loss due to moisture in air (H2O) L5. Loss due to carbon monoxide (CO) L6. Loss due to surface radiation, convection and other unaccounted. L7. Unburnt losses in fly ash (Carbon) L8. Unburnt losses in bottom ash (Carbon) Boiler Efficiency by indirect method, = 100 – (L1 + L2 + L3 + L4 + L5 + L6 + L7 + L8)

Factors Affecting Boiler Performance Periodic cleaning of boilers Periodic soot blowing Proper water treatment programme and blow down control Draft control Excess air control Percentage loading of boiler Steam Generation pressure and temperature Boiler insulation Quality of fuel

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