How to improve Thermal power plant efficiency??

Power plant efficiency is the ratio of output X 100 / Input

Power plant performances are measured in terms of heat rate. Heat rate is the amount of heat required to generate 1 KWH of power.

So power plant efficiency = 860 X 100 / Heat rate.

Where, 860 is heat value of 1 KWH power (1 KW = 860 kcal)

So it is clear that, to increase the power plant efficiency, we need to reduce the heat rate.

Thermal Power plant heat rate can be calculated from the following formula

THR (Thermal PP) = Fuel consumption X GCV / Power generation

Again, from the above formula it is clear that, heat rate of thermal power plants can be reduced by reducing the fuel consumption & increasing the power consumption.

And also heat rate of the process plant is calculated as,

THR (Process plants) = ((Fuel consumption X GCV + Heat content in DM water make up + Return condensate from process plants) –(Heat content in steam given to process plants)) / Power generation.

From the above formula, it is clear that, heat rate of the process plants can be reduced by

1-Reducing fuel consumption

2-Reducing DM water consumption

So to reduce heat rate of any power plant, need to concentrate on following areas.

                                    Buy Now

A-Reduction of fuel consumption of steam generators (Boilers):

Increase in fuel consumption is the major reason to increase plant heat rate & hence reduction of power plant as well as Boiler efficiency.

Need to exercise on following areas to reduce fuel consumption

1-Use of high GCV fuel (as per design):

Fuel consumption = Steam generation X (Steam enthalpy-Feed water enthalpy) / (Boiler efficiency X Fuel GCV)

By looking at the above relation, Boiler fuel consumption reduces on

a-Using high GCV fuel

b-Operating the Boiler at rated pressure & temperature

Please note that, For every 100 kcal/kg increase in GCV of coal, boiler (TG) efficiency increases by 0.36% and vice versa.

 

2-Reduction of use of excess air:

Excess air more than required leads to heat loss due to dry flue gas. Excess air can be reduced by

a-Selecting low moisture fuel

b-Optimum GCV fuel

c-Selecting the fuel with optimum hydrogen & ash contents

d-Operating the Boilers with non-competent persons

e-Wrongly tuned air & fuel mixture

F-Absence of Oxygen analyser at Boiler outlet ducts. Excess air cab ne monitored by O2 analysers & accordingly air can be controlled.

Please note that,

• For every 5% increase in excess air for bagasse, boiler efficiency decreases by 0.18% and vice versa.
• For every 1% increase in bagasse moisture, boiler efficiency reduces by 0.27% and vice versa.
• For every 0.5% increase of Hydrogen in bagasse, boiler efficiency decreases by 0.8–1% and vice versa.

3-Redution of unburnts in ash.

• Unburnt in ash is due to improper combustion
• Low GCV & high ash & moisture in fuel
• Improper operation of the Boiler

Unburnt in the ash can be reduced by

• Selecting required quality of fuel having optimum ash & moisture
• Maintaining proper excess air. Less excess air for high moisture fuel may lead to improper combustion.
• Achieving 3Ts of combustion (Temperature, Turbulence & Time)
• Operation of the Boilers by competent operators

For more information read; 10-tips to reduce Boiler LOI

4-Maintaining feed water temperature as per design

On every 6-8 degree C rise in feed water temperature, fuel consumption of the boiler reduces by 1%.

Refer below formula

Fuel consumption = Steam generation X (Steam enthalpy-Feed water enthalpy) / (Boiler efficiency X Fuel GCV)

Feed water enthalpy increases as its temperature increases.

Feed water temperature can be increased by increasing by adopting regenerative cycles (use of HP & LP heaters)

5-Other exercises to reduce boiler fuel consumption are;

a-Reduction of Boiler outlet flue gas temperature

b-Optimizing Boiler blow downs

c-Reducing convective & radiant heat losses

d-Operating soot blowers regularly to remove heating surface external scales

e-Use of quality water to avoid internal scaling

f-Operating the Boilers at maximum loads (80 to 100% of MCR)

g-Arresting all flue gas, air & steam leakages in the Boilers

Read 16-Perfect reasons for more fuel consumption of Boilers

B-Reduction of steam consumption by Steam Turbines (prime mover)

More steam consumption by steam turbines to generate unit power leads to more het rate of Turbine as well as plant. So it is utmost important to reduce steam consumption.

Following actions needs to take to reduce steam consumption for generating unit power.

• Maintaining designed vacuum in steam condensers. Operating the Turbines at lower vacuum results into more specific stem consumption
• Operating the Turbine at maximum possible load
• Operating the Turbines at rated pressure & temperature
• Carrying out of STG maintenance as per OEM schedule. More clearance in labyrinth seals lead to high exhaust temperature & reduction in vacuum
• Regular maintenance of steam jet ejectors & vacuum pumps
• Maintaining proper temperature & pressure at bleed steam lines
• Improving the cooling tower efficiency

For more details read; Reasons for more specific steam consumption of a steam Turbine

C-Reduction of losses in steam lines & reuse of trap/drains condensate

Arresting of steam losses through leakages, drains & traps. And installing drain/trap condensate recovery system to improve cycle efficiency.

For example loss of 1000 kg of condensate at temperature 80 deg C leads to fuel (coal) consumption of

Assumptions: Atmospheric temperature 25 deg C, Fuel GCV 4500 kcal/kg & Boiler efficiency 80%.

 

Mf = 1000 X 1 X (80-25)/(Boiler efficiency X Fuel GCV)

Mf =1000 X 1 X 55 / (0.75 X 4500) = 16.3 kg of coal

Other losses include

Optimization of deaerator vent steam flow.

D-Other miscellaneous

• Carrying out regular maintenance of traps & drain valves to avoid passing & leakages
• Applying insulation to all hot uninsulated lines
• Incorporating VFD drives to fuel feeding system, Boiler fans, cooling water pumps & cooling tower fans for controlling operation & to use resources as per requirement
• Selecting the competent operation & maintenance team
• Conducting regular trainings to the field team
• On job trainings & tool box talks will help to optimize the resource utilization & knowledge up gradation for proper operation
• Selection of proper equipments & system as per plant suitability
• Adopting all advanced automation in plant operation

 

 For related articles read;

Power plant & calculations

Boiler calculations for BOE exam