Improving efficiency, saving boiler energy is an urgent matter of concern to businesses, especially in the present time, when fuel prices tend to increase.
There are many measures to improve energy efficiency in the boiler system related to combustion, heat transfer, energy loss, and reducing power consumption of supporting equipment. By checking some of the following conditions, it can help businesses evaluate whether their boiler equipment is operating at maximum efficiency.
Please read with KS – Boiler to learn measures to help you save energy and use boiler effectively!
Temperature control of boiler gas
The boiler gas temperature should be as low as possible. However, this temperature should not be so low that the water vapor in the exhaust pipe condenses on the wall of the pipe. This is important for fuels with a high sulfur content because low temperatures will lead to corrosion due to sulfur fogging. Furnace gas temperatures higher than 200°C indicate potential for waste heat recovery. Such high temperatures also indicate deposits in the heat transfer/recovery equipment, so early blowdown is required to clear the water/steam.
Preheating of feed water using heat exchanger
Normally, the flue gas of a 3-stage clamshell boiler has a temperature of about 200 to 300 °C. Therefore, there is potential for heat recovery from the furnace gas. The flue gas temperature from the boiler is usually maintained at a minimum of 200°C, so that the sulfur oxide in the flue gas does not condense and cause corrosion at the heat transfer surface. When using clean energy such as natural gas, LPG or oil, the economic benefits from heat recovery will be higher because the furnace gas temperature can be maintained below 200°C. The potential for energy savings depends on the type of boiler and fuel used. With a typical old clamshell boiler, with a flue gas temperature of 260°C, an Economizer can be used to reduce it to 200°C, increasing the feed water temperature to 15°C. Total thermal efficiency can be increased by 3 %. With a 3-stage clamshell boiler using advanced natural gas, the flue gas temperature is 140°C, using a condenser heat exchanger will reduce the temperature to 65°C, increasing the thermal efficiency by 5%.
Preheating the boiler supply air
Preheating the boiler supply air is an alternative to water preheating. To increase the thermal efficiency by 1 %, it is necessary to increase the combustion gas temperature by 20°C. The majority of oil and gas burners used in boiler lines are of designs that are not suitable for high preheating temperatures.
Modern incinerators can withstand much higher preheating temperatures, so it is advisable to use this unit as an exhaust heat exchanger as an alternative to an economizer, when space is available. or the high feed water recovery temperature meets the requirements.
Incomplete combustion
Incomplete combustion may be due to lack of air or excess fuel or improper fuel allocation. Incomplete combustion can be clearly seen if color or smoke is observed and immediate correction is required.
In the case of an oil or gas combustion system, CO or smoke (for oil-fired systems only) with normal or high residual gas levels indicates system problems. A common cause of incomplete combustion is the wrong mixture of fuel and air in the burner. Poor burning oil can be caused by non-standard viscosity, clogged burners, burner carbonization and diffuser degradation.
With a coal-fired boiler, unburnt carbon can lead to huge losses. This happens when there is carbon in the slag and increases the boiler heat supply by more than 2%. Uneven coal size can also be a cause of incomplete combustion. In the chain burner, the large coal particles will burn out, and the small and fine particles will clog the air passage, causing uneven air distribution. With blast chambers, excessive wind and combustion regulation can affect carbon loss. Increasing the amount of fine particles in crushed coal can also cause carbon losses.
Residual gas control
The table below gives the theoretical mass of gas required to burn with different fuels. In all practical cases, an excess of gas is required to ensure complete combustion, to allow for errors in combustion, and to ensure suitable furnace gas conditions for some fuels. Optimal residual air for the highest boiler efficiency is when the total loss due to incomplete combustion and loss due to waste heat through the flue gas is minimized.
This level of residual gas can vary depending on furnace design, furnace type, fuel, and process variables. This level of residual gas can be determined through tests with different gas-fuel ratios.
Minimize heat loss due to radiation and convection
The outer surface of the clamshell boiler is hotter than the surrounding. As a result, this surface will experience heat loss to the surroundings, depending on the surface area and the temperature difference between the surface and the surroundings.
Heat loss in a clamshell boiler is usually a fixed energy loss independent of the boiler output. In modern design boilers, this loss can be as little as 1.5% of total heat capacity at peak, but increases to around 6%, if the boiler is operating at only 25% of output.
Repairing or enhancing insulation will help reduce heat loss through boiler walls and pipes.
Automatic blowdown control
Uncontrolled continuous blowdowns will be very wasteful. Therefore, it is recommended to install automatic blowdown control devices, corresponding to boiler water conductivity and pH. Every 10% blowdown at a 15kg/cm2 boiler will result in a performance loss of 3%.
Reduced loss due to sludge and soot
In coal- and oil-fired boilers, soot adheres to the tube, which is an insulating element, hindering heat exchange. Soot should be removed on a regular basis. The increase in flue gas temperature may be due to excessive soot accumulation.
Sediment has the same effect on water. High flue gas temperatures with normal residual gas levels indicate poor heat transfer performance. Poor heat transfer performance can be caused by soot or deposits. With water deposits, it is necessary to review the water treatment process and clean the pipes. It is estimated that every 22°C increase in furnace gas temperature will cause an estimated 1 % heat loss. The furnace air temperature should be checked and recorded regularly as this number reflects the amount of soot deposited. When the furnace gas temperature exceeds the temperature of the newly cleaned boiler by about 20°C, it is also time to remove the soot. Therefore, it is recommended to install a scale thermometer at the place where the chimney is located to monitor the exhaust gas temperature.
It is estimated that a 3 mm thick layer of soot will increase energy consumption by 2.5% due to an increase in furnace gas temperature. It may be necessary to periodically stop the line to clean the radiator surfaces, tubes, Economizers, and air dryers to remove these nasty soots.
Reduce boiler pressure
This is an effective way to reduce fuel consumption, if possible, by between 1 and 2 %. The lower steam pressure reduces the saturation steam temperature and does not recover the flue gas heat, and the flue gas temperature is similarly reduced.
Vapors are typically formed at the highest pressure/temperature level of a given process. In some cases, the process does not operate continuously, and there are times when furnace pressure can be reduced. But also remember, reducing boiler pressure reduces the specific volume of steam in the furnace, and effectively removes air from the boiler outlet, carrying water. The company’s energy officer should consider the effects of pressure reduction carefully before recommending implementation. The pressure should be reduced in stages, and should not be reduced by more than 20 %.
Boiler Load Control
The maximum efficiency of the boiler is not achieved at full load, but at 2/3 full load. If boiler load is reduced further, efficiency also tends to decrease. At zero output, the boiler efficiency is zero, and the burning fuel will only produce losses. Factors affecting boiler efficiency include:
– When the load is reduced, the flue gas flow value through the tubes also decreases. As the air flow decreases with the same heat transfer area, the furnace gas temperature will be slightly reduced, reducing heat loss.
– At below half-load, igniters need more excess air to burn off the fuel. Therefore, heat loss increases.
In general, boiler efficiency can drop significantly below 25% load and boiler operations below this level should be avoided as little as possible.
Replacing the boiler
The potential savings from boiler replacement depends on the change in the expected total efficiency. Financially, the boiler replacement solution will be very attractive if the boiler in use has the following factors:
– Old and ineffective
– Cheaper alternative fuels cannot be used.
– Size is too big or too small for current requirements
– Not designed for ideal load conditions
KS – Boiler specializes in manufacturing, installing and maintaining industrial boilers:
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