A condensing boiler can condense the water vapour in the flue gases and withstand the corrosive and acidic qualities of the flue gas condensate. Although most boilers can condense the flue gasses, only boilers that have heat exchangers constructed from materials able to withstand the corrosion should be used in condensing application. Condensing boilers with primary and secondary heat exchanger do not work well as they are not able to fully condense and defeat the purpose of using a condensing boiler. Also, boilers with this arrangement are prone to condensation in the primary heat exchanger at lower firing rate which can cause damage to the heat exchanger.
Shell boilers may be defined as those boilers in which the heat transfer surfaces are all contained within a steel shell. Shell boilers may also be referred to as "fire tube" or "smoke tube" boilers because the products of combustion pass through the boiler tubes, which in turn transfer heat to the surrounding boiler water.
The vertical type and horizontal type are the two main types of boiler. The vertical gas-fired boiler has small volume and is suitable for small workshops or small production enterprises. It is often used in the fields of hot water and heating. The horizontal gas-fired boiler has larger volume with a wider application range than the vertical gas-fired boiler.
Due to the development of boiler technology and relevant policies, gas-fired boilers using eco-friendly fuels are often applied for heating. For thermal power companies, cost is the most important issue.
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.
