How to Calculate Boiler Efficiency?
To calculate boiler efficiency, we use the following formula:
Boiler efficiency = (Heat Output ÷ Heat Input) x 100.
Given parameters (for example):
Boiler capacity = 7 tons/hr
Steam pressure = 7 bar
Steam temperature = 165°C
Feedwater temperature = 40°C
Feedwater pressure = 1 bar
Fuel (input material) = Rice husk
Fuel feed rate: 1,200 kg/hr
Calculation Steps:
1. Convert boiler capacity from tons to kg/hr
Formula: Multiply the boiler capacity (tons) by 1000 (kg/ton) = 7 x 1000 = 7,000 kg/hr.
2. We need the enthalpy of steam at a given temperature and pressure
As per steam tables, the enthalpy of steam at 165°C and 7 bar pressure is approx. 2,764 kJ/kg
(Ref: enghandbook.com). Steam enthalpy varies with temperatures and pressures.
3. We need the enthalpy of feed water at a given temperature and pressure
As per water property tables, the enthalpy of feedwater at 40°C and 1 bar pressure is approx. 167 kJ/kg
(Ref: enghandbook.com). Water enthalpy varies with temperatures and pressures.
4. Calculate the actual enthalpy of steam
Actual enthalpy value of steam = Steam enthalpy – Feedwater enthalpy = 2,764 – 167 = 2,597 kJ/kg.
5. Calculate the energy content of the input material in kJ/kg
Energy content of the input material = GCV of the material (e.g., rice husk): 4,000 kcal/kg.
To convert kcal/kg to kJ/kg, multiply kcal/kg by 4.184 (conversion factor) = 4,000 x 4.184 = 16,736 kJ/kg.
6. Calculate heat input:
Heat input = Material feed rate (kg/hr) x Material energy content (kJ/kg) = 1,200 x 16,736 = 20,083,200 kJ/hr.
7. Calculate heat output:
Heat Output = Boiler capacity (kg/hr) x Actual enthalpy of steam (kJ/kg) = 7,000 x 2,597 = 18,179,000 kJ/hr.
8. Boiler efficiency calculation:
Boiler efficiency = (Heat output ÷ Heat input) x 100 = (18,179,000 kJ/hr ÷ 20,083,200 kJ/hr) x 100 = 90.51%.
Frequently Asked Questions
GCV (Gross Calorific Value)
1. What is GCV?
GCV is the total amount of energy released when a fuel is burned, including the energy used to vaporize water.
2. How is GCV calculated?
GCV is typically calculated through laboratory tests, such as bomb calorimetry.
3. What is the difference between GCV and NCV (Net Calorific Value)?
NCV is the energy released minus the energy used to vaporize water, while GCV includes this energy.
Enthalpy
1. What is enthalpy?
Enthalpy is a measure of the total energy of a system, including internal energy and pressure-volume work.
2. How is enthalpy calculated?
Enthalpy is calculated as H = U + pV, where U is internal energy, p is pressure, and V is volume.
3. What is specific enthalpy?
Specific enthalpy is the enthalpy per unit mass of a substance.
Biomass
1. What is biomass?
Biomass is organic matter from plants or animals used as fuel or energy source.
2. What are the benefits of biomass energy?
Biomass energy is renewable, can reduce greenhouse gas emissions, and provides energy independence.
3. What are common types of biomass?
Common types of biomass include wood, agricultural waste, and waste from forestry or paper industries.
Kilo Joules (kJ)
1. What is a kilo joule?
A kilo joule is a unit of energy, equivalent to 1000 joules.
2. How are kilo joules used?
Kilo joules are used to measure energy content, heat transfer, and work done in various applications.
3. What is the relationship between kilo joules and other energy units?
1 kJ = 0.239 kcal (kilocalories) or 1 kJ = 0.948 BTU (British Thermal Units)
Other
1. What is the difference between heat input and heat output?
Heat input is the energy added to a system, while heat output is the energy released or transferred.
2. How is boiler efficiency calculated?
Boiler efficiency is calculated as (Heat Output / Heat Input) x 100.
3. What are common applications of thermodynamics?
Thermodynamics is applied in power generation, refrigeration, heat transfer systems, and more.
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