Denitration issues in CFB boilers

This post was last edited and replied to by dongjiang1001 on 2011-10-10 at 12:44. Reply 1# kof369: Circulating fluidized bed boilers do not require desulfurization devices; desulfurization is achieved simply by adding limestone. Their cost is already very high, and if desulfurization or other such devices are added, it would be better to use a conventional furnace instead. Due to flue gas recirculation, circulating fluidized bed boilers have a relatively low combustion temperature, which suppresses the formation of thermally induced NOx. There is no need for a denitration device; room-type burners must be equipped with desulfurization and denitration systems.

According to the **newly issued emission standards for air pollutants from thermal power plants, the requirement at the outlet of fluidized bed boilers is 200 mg/NM3; in key areas, this figure is 100 mg/NM3. Fluidized bed boilers are designed with low nitrogen emissions, so the concentration of nitrogen oxides is also around 100 (very low), with maximum values reaching a little over 400. So denitration is also required. SNCR is generally used for denitration, with a denitration efficiency in the range of 50-70%. Several projects are already under construction or have been completed in the country.

It will be necessary to install denitration equipment within two years; urgent solutions are needed

This is a good question; I suggest the moderator pin this post

Reply to 1# kof369: I’m sorry, OP; I might not have noticed the change in policy before. CFB boilers will soon be subject to off-market sales. “The 12th Five-Year Plan set much higher requirements for eliminating stockouts. Sources from the five major power companies told a reporter from China Securities Journal that the agreement will stipulate that during the 12th Five-Year Plan period, these companies will reduce sulfur dioxide emissions by 16% and nitrogen oxide emissions by around 35% compared to the levels during the 11th Five-Year Plan period (with slight variations among different power companies). It is understood that in addition to the five major power groups, those who signed the responsibility letter this time include CNPC, Sinopec, State Grid Corporation, as well as some local authorities. Industry experts believe that this incident has two implications: first, the emission reduction targets set by the five major power companies far exceed expectations, which is a significant boon for the domestic desulfurization and denitrification industry. Secondly, a significant increase in targets means that the five major power companies will have to increase their investments in emission reduction. Given the severe losses suffered by these power companies, it becomes even more urgent to raise electricity prices in the near future or to introduce special pricing for denitrification efforts. SNCR should be able to be used for off-gas treatment, with the reactants being injected mainly from above the burner, near the furnace outlet. There are many explanations for this principle on Baidu. Now, SCR technology is also quite mature; most boiler manufacturers are able to integrate it into the boiler, located after the economizer and before the air preheater.

As far as I know, air preheaters used for denitration via the SCR method must be rotary; generally, air preheaters in circulating fluidized bed boilers are tubular, so SCR may not be suitable for circulating fluidized bed boilers

Circulating fluidized bed boilers use low-temperature combustion, and measures can be taken within the boiler to reduce the formation of NOx; as a result, their NOx emissions are much lower than those of coal-fired boilers. According to available data, coal-fired boilers without denitration systems can have NOx emissions as high as 800–1500 mg/m3, which far exceeds the newly established emission standards. In contrast, due to low-temperature combustion and the possibility of using techniques such as staged combustion and low-oxygen combustion to suppress NOx formation, circulating fluidized bed boilers can achieve NOx emission concentrations of 100–200 mg/m3, which is essentially in line with the newly set environmental emission standards. If the flue gas emissions of circulating fluidized bed boilers exceed the allowable levels due to factors such as fuel changes or boiler design, appropriate denitration processes can be employed; even with lower denitration efficiency, these processes can still meet environmental regulations, thereby saving on investment and operating costs.

Currently, the standards for NOx emissions are 100 and 50; CFB boilers need to be equipped with SCR systems in order to meet these standards.

The project we are working on now involves denitration using the SCR method. The client requires a tubular preheater, but in reality, for the SCR method, a rotary air preheater is more suitable.

This problem has become the biggest issue for industrial boilers today, especially small ones. The equipment available on the market is not yet fully developed, and its cost is high; for new small boilers, installing such equipment significantly increases the overall cost. It’s not possible to do so without an increase; otherwise, approval simply won’t be granted.