Efficiency in Generation & Utilization ofSteam

Energy consumption in India

More than 70% of the total energy consumed in India is converted to steam and the same is utilized inElectrical Power generationProcessProcess heating

Power generationAround 65% of the total power generation i.e. 1,53,694 MW, in India, is obtained through thermal route.

Hence the efficiency in generation & utilization of steam plays a crucial role in our goal of EC.

Steam GenerationThe losses associated in the generation of steam are ~ 15%.The principal losses are,Loss of heat due to dry flue gasLoss of heat due to moisture in fuel and combustion airLoss of heat due to combustion of hydrogenLoss of heat due to radiationLoss of heat due to unburnt

The major factors responsible for these lossesFuel combustionHeat recovery Steam & condensate management.

Steam GenerationFuel Combustion

Particle size

Air & Fuel mix up

Draft control

Temperature

Steam GenerationThe Combustion efficiency depends on the extent of excess air required to ensure complete combustion.

Higher the excess air, higher the dry flue gas losses.

Lower the excess air, higher the un-burnt losses.

Therefore it is essential to optimise the excess air quantity, for a particular load conditions of a boiler.

Steam GenerationOptimization of excess air can be done by conducting tests, at various air-fuel ratios, to determine the sum of losses due to incomplete combustion & dry flue gas losses.

Generally it is suggested that, Excess air can be best optimized if there is facility to monitor CO in flue gases.

Steam GenerationHeat recovery from hot flue gases.

Generally heat from the hot flue gases are recovered by feed water heating in the economiser and air preheating.

The effluent flue gases are cooled in the process up to ~130 0C.

If these gases are cooled to ~100 0c, the losses will reduce by ~ 1.5%.

Steam GenerationHeat recovery from hot flue gases.

Out of the heat supplied to the furnace ~ 21% is recovered in economiser and ~9% in APH.

The moisture present in the flue gases in coal fired boilers is ~10% (v/v).

The dew point of flue gases with humidity as above will be < 80 0c.

Steam Generation

The flue gases are cooled to such low temperatures, as to condense part of the humidity to improve the overall efficiency, through CHX technology, where Teflon coated heat exchange equipment, FRP ducting & chimneys are installed.

This technology is in use in cold countries, where the waste heat is more effectively recovered.

This may be more useful in oil/gas fired boilers where the humidity of flue gases is high.

CHX Technology In general 11% heat loss occurs in steam generators through hot flue gases.Acid dew point of flue gases compels us to leave the flue gases at higher temperature.Acid dew point of flue gases depends on the sulfur content of fuel.If flue gas temperature falls below this, cold end corrosion will start.In CHX technology flue gas path is covered with specially extruded TEFLON both on shell & tube side so that cold end corrosion is avoided in spite of reduction in flue gas temperature.This is a proven technology & in use in USA for over two decades.This is to be incorporated in the design stage of the plant itself.

HEAT RECOVERY IN SG Losses=12.6%1.0%0.5%11.1%

HEAT RECOVERY IN SG Losses=12.6%1.0%0.5%11.1%

Power Generation

The efficiency in conversion of steam to power is estimated through Heat rate, which depends on, Co-generationLosses in piping & valves.Design operating conditions.Steam & condensate management

Power generation

Co-generation

It is the simultaneous generation of heat & power.

The overall efficiency of a system is higher since the heat produced is more effectively utilised.

In conventional power plants, where the heat to power ratios are small, the efficiencies are less i.e., the heat rates are higher.

In captive power plants, which meet the larger thermal requirements of the process, high heat to power ratios are achieved and accordingly higher efficiencies.

Power generation

Heat Rate

Heat rate is the ratio of the total heat supplied to the net heat recovered.

Generally expressed as the total heat supplied to generate one unit of power in Kcal/Kwh.

If the efficiency of a system is the net heat recovered per unit of heat supplied, the heat rate is reciprocal of efficiency.

It depends on the ratio of power generated through condensing steam route and to that of extraction steam route.

Higher the ratio, higher the heat rate, i.e lower conversion efficiency.

Higher efficiencies are achieved in co-generation systems.

Power generation

Improvement in heat rates

Through increased cogeneration effect.

This can be achieved by extracting more heat for condensate/feed water reheating.

This will help in improved heat rates of TG besides overall reduction in heat supplied to the boiler furnace.

Higher feed water temperatures demand low heat duties of economisers, which can be compensated by intermediate steam reheating.

Heat RateHeat Rate = Net heat recovered as KWHTotal Heat supplied as Kcal(H2 H1) (H4 H5)(H2 H1) =~

Power generation

Losses in piping & valves

Around 5 bar drop in the piping & valves between Boiler & TG will lead to ~0.7% fall in isentropic efficiencies of TG.

These losses will be still higher, when different combinations of Boiler & TGs are in operation.

Design operating conditions Optimization of design parameters.

Deviation from design conditions.

Part load operation.

Design operating conditions Optimization of design parameters.

Based on the thermal utility requirements & their optimized operating conditions, the design parameters of the TGs be optimized.

Any deviation either at the thermal utility end or at TGs will lead to higher inefficiencies.

Steam & condensate managementTotal recycle of condensate through effective steam & condensate management will help in minimizing losses through boiler blow downs as a result of minimal make up requirements.

Boiler Make up waterAn indirect measure of inefficiency in use of steam. Attributable for steam, condensate losses.Higher blow down lossesIdeally, the makeup is required only to meet the de-aeration vent steam losses & associated blow down.

Steam networkLook for steam & condensate leaks.

The slope of the line in the direction of flow should be a minimum of 100 mm for every 25 M of length.

Drain points at every 40 M length of the piping and also at the lowest points.

Drain points are with equal tee connection only.

The branch lines are tapped from top of the mains.

Steam networkThe utility heaters / equipment are not very far from the mains.

Healthiness of steam traps.

Lowest possible pressure at the point of utility.

Insulation of steam piping. Flanges & valves. An un insulated flange in a 150 mm steam pipe, consumes ~ 1 Te additional coal per year.

InsulationRepair damaged insulations.

Replace wet insulation.

Ensure proper cladding of insulation.

Ensure proper insulation of flanges, valves & other piping accessories.

In-house powerIt is generally 8 to 10% of the plants power generation and constitutes of following-Pump & fan power.

Power for fuel transportation.

Power for fuel preparation.

Air conditioning power.

In-house powerPump & fan power. This constitutes the major part of in-house power, and includes power for handling feed water, cooling water, service water, fire water, combustion air, flue gas, service air, instrument air, etc.Properly optimize the design parameters of the pumps & fans.Ensure that the pumps & fans are operating at their best efficiency point.Avoid unwanted throttling, recirculation, leakages, etc.Utilise VFDs

In-house powerPower for fuel transportation. Select the economical & energy efficient mode of transportation, considering the installation & operating cost of various options like road, rail, conveyor, aerial rope way, etc.Distance from the pit head to power plant, local political scenario, environmental conditions, existing connectivity, etc needs to be considered while selecting the mode of fuel transportation.Coal washeries & de-sulfurization plants better to be located near to pit head.

In-house powerPower for fuel preparation. Select the best means of fuel preparation i.e coal mills, crushers, heaters etc., based on the quality & quantity of fuel handled.

Ensure that they will be optimally loaded irrespective of the plant load. This requires going for more mills per boiler.

Select the minimum possible temperature for fuel oil transport.

In-house powerAir conditioning power.

Go for the vapor absorption based air conditioning system using steam extracted from TGs at best optimized pressure.

This will not only save the energy in operating A/C system, it will also improve the co-generation effect leading to better Heat Rate.

Thank you