Gas-fired hot water boilers require high-quality water to improve the boiler performance and extend the service life. If the boiler uses the tap water of water which contains a lot of impurities, magnesium and calcium ions in the water will form white precipitates when the water is heated at high temperatures, which can cause the scaling problem to reduce the heat transfer efficiency of the boiler and bring hidden dangers of the boiler safety.
The gas-fired hot water boiler heats up quickly and has the high thermal efficiency. It is widely used in the heating industry and production. What are the maintenance methods of the gas-fired hot water boiler?
Combustion efficiency is an indication of the burner’s ability to burn fuel. The amount of unburned fuel and excess air in the exhaust are used to assess a burner’s combustion efficiency. Burners resulting in low levels of unburned fuel while operating at low excess air levels are considered efficient. Well designed conventional burners firing gaseous and liquid fuels operate at excess air levels of 15% and result in negligible unburned fuel. Well designed ultra low emissions burners operate at a higher excess air level of 25% in order to reduce emissions to very low levels. By operating at the minimum excess air requirement, less heat from the combustion process is being used to heat excess combustion air, which increases the energy available for the load. Combustion efficiency is not the same for all fuels and, generally, gaseous and liquid fuels burn more efficiently than solid fuels.
Excess air provides safe operation above stoichiometric conditions. A burner is typically set up with 15% to 20% excess air in higher firing ranges. Higher excess air levels result in fuel being used to heat the air instead of transferring it to usable energy, increasing stack losses and significantly decreasing efficiency. Boilers with lower excess air throughout the operating range have higher efficiencies.
In theory, to have the most efficient combustion in any combustion process, the quantity of fuel and air would be in a perfect ratio to provide perfect combustion with no unused fuel or air. This type of theoretical perfect combustion is called stoichiometric combustion. In practice, however, for safety and maintenance needs, additional air beyond the theoretical "perfect ratio" needs to be added to the combustion process - this is referred to as "excess air".
This is because, under normal circumstances, the exhaust temperature of the boiler cannot completely condense the water in the flue gas, and the difference between the low calorific value and the high calorific value is mainly in the part of the latent heat of vaporization, so the low heat is used. The value is calculated to reflect the true efficiency of the boiler. However, there will be some special circumstances. For example, if the boiler is a condensing boiler, the calculation of the condensed water portion should be calculated using the high calorific value.
Reliability is absolutely essential to optimal boiler performance. In order to achieve the highest degree of dependability in a boiler it is important to identify and address the primary causes of boiler problems. One of the most common issues that can compromise a boiler is poor water quality.
The effect of water quality on boiler performance is a huge concern for plant owners and operators. Premature boiler failure often occurs as a result of poor or inconsistent feed water quality. Hard water elements in feed water are responsible for a number of issues:
Steam carries about 540 Kcal/kg of useful energy whereas hot water and thermal fluid carry much less energy. Steam does not require a pump to transfer the energy. Generally, if the heating temperatures required are <100°C, then hot water can be used and if temperatures >180°C are needed then thermal fluid might be a better choice. For process temperatures between 100°C and 180°C steam is considered a viable option.
