1. Introduction
With the continuous tightening of national environmental policy, boiler nitrogen oxide (NOx) emission limits are increasingly stringent. A low-nitrogen boiler has become the necessary equipment in industrial production, commercial heating and other fields. Many enterprises in the selection of both fear can not meet the requirements of the new regulations, but also worry about increased costs. In fact, the selection of low-nitrogen boilers can not only easily comply with regulations, but it can also reduce cost and increase efficiency by optimizing energy consumption. From the four dimensions of core index, combustion technology, system compatibility and policy subsidy, we can sort out the key points of low-nitrogen boiler type selection
Focus on the Core Indicators: NOx Emissions
At present, the mainstream standards implemented nationwide are divided into two categories: One is NOx emission ≤ 30mg/m³.It is suitable for first-tier cities and key industrial parks with strict environmental protection requirements, such as Beijing, Shanghai and Guangzhou. Some places have also introduced more detailed local standards, Enterprises should give priority to meet this target.
The other is NOx emission ≤ 50mg/m³. Covering most second- and third-tier cities and non-key control areas, meet the latest requirements of the National Boiler Air Pollutant Emission Standard (GB 13271-2014).
2. Comparison of Low-Nitrogen Combustion Technologies and Their Adaptable Scenarios
Full premixed combustion technology. By mixing gas and air in advance, To ensure more uniform and adequate combustion, NOx emissions can be easily controlled below 30mg/m³, and thermal efficiency can reach more than 96%. It is suitable for commercial buildings (such as hotels, hospitals) and small and medium-sized industrial scenes with high environmental requirements and energy efficiency. The advantages of this technology are stable operation, low noise and low maintenance costs, but it requires high precision for gas purity and air ratio. Initial equipment procurement costs are slightly higher.
The staged combustion technology reduces NOx formation by reducing the local combustion temperature through feeding the gas into the furnace in stages. Emissions are usually around 50mg/m³, thermal efficiency is about 92%-94%, Suitable for moderate environmental requirements, large fluctuations in working conditions in the industrial field (such as food processing, textile). It is characterized by strong adaptability, moderate equipment costs and simple maintenance, but attention should be paid to the furnace structure design to avoid coking caused by local high temperatures.
The flue gas cycle combustion technology is to send part of the low temperature flue gas back to the furnace, mix with fresh air and participate in combustion, reduce the combustion temperature and oxygen concentration. NOx emission can be controlled at 30-50mg/m³, thermal efficiency is about 93% -95%, suitable for large industrial boilers (such as chemical industry, electric power). The advantages of this technology are that it is easy to retrofit and suitable for low-nitrogen retrofitting of the original boiler, but it needs additional flue gas circulating fan, which will increase a small amount of energy consumption.
3. Evaluation of System Compatibility
Circumstances where renovation is prioritized: If an enterprise's existing boiler has a short service life (no more than 5 years) and its body structure is intact, the enterprise can prioritize low-nitrogen retrofitting, low nitrogen emission can be achieved by replacing burner and optimizing furnace structure. The retrofit cost is usually 30% -50% of the newly purchased equipment. And the retrofitting cycle is short (about 1-2 weeks), can reduce the loss of production.
Circumstances where new purchase is recommended: However, it should be noted that some old boilers (service life of more than 10 years) due to body corrosion, low thermal efficiency, After the transformation may not meet the expected environmental protection and energy efficiency standards, but will increase the late maintenance costs, in this case the transformation is not recommended. If the existing boiler aging serious, high energy consumption, or enterprises have to expand production capacity demand, it is recommended to buy new low-nitrogen boiler. Although the early investment of newly purchased equipment is high (about 100,000-500,000 yuan for small and medium-sized boilers and more than one million yuan for large industrial boilers), but enjoy a longer life (usually 15-20 years) and better energy efficiency, lower long-term operating costs.
Considerations for system compatibility: The new boiler can be customized according to the existing pipes, pumps, heat exchangers and other systems, stronger compatibility, avoid the waste of energy caused by the mismatch of the system.
4. Make Full Use of Policy Subsidies
To promote the popularization of low-nitrogen boilers, the state and local governments have introduced a number of subsidy policies. Enterprises can take the initiative to apply for subsidies during the selection process to further reduce costs. Application should pay attention to two key points. Firstly, the subsidy application has a time limit, usually a fixed annual filing cycle, enterprises need to pay attention to the policy notice in advance. Secondly, some areas require the boiler to enter the local recommended directory, select the preferred products in the directory, can improve the success rate of subsidy application. In addition, Some provinces have also introduced supporting policies such as low-interest loans and tax breaks, so enterprises can make comprehensive use of various policies, enterprises can make comprehensive use of a variety of policies, reduce type selection and operation cost to the greatest extent.
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