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What's So Hard About 'ultra-low Emissions' Of Biomass?
- Jul 04, 2018 -

On June 26, the ministry of ecology and environment announced the progress of strengthening supervision and inspection of key areas of the 2018-2019 blue sky defense war.According to the report, 473 coal-burning boiler enterprises should be eliminated from the inspection list, and two coal-burning boilers, accounting for 0.4% of the total, were found to be inadequate.9 coal-fired boilers should be eliminated from the list.

With the increasingly severe environmental protection requirements, the elimination and rectification of some coal-fired boilers have attracted increasing attention.In many provinces and regions, biomass is becoming an effective supplement and alternative fuel for coal.With the continuous advancement of the "ultra-low emission" of coal-fired boilers, the biomass with missing emission standards often needs to face the same "ultra-low emission" test.

Can biomass meet the "ultra-low emission" standard of coal burning?What are the technical difficulties?Is it economical?

How does denitrification meet the standard?

"When the company first used biomass boilers around 2007, it implemented the 2003 national standard."The content of nitrogen oxides, sulfur dioxide and soot shall not exceed 200mg/m3, 100mg/m3 and 50mg/m3 respectively, according to the 2003 standards for the emission of atmospheric pollutants in thermal power plants (gb13233-2003).Han mou, head of a jiangsu biomass enterprise, told reporters that it was not difficult to meet the emission standards.

But starting in 2013, 19 provinces (autonomous regions and municipalities) of 47 ground level and above city was listed in key control area, thermal power, steel, petrochemical, cement, nonferrous metal, chemical industry and so on six big heavy pollution industry and coal-fired industrial boilers to implement special emissions limits.The emission standards of nitrogen oxides, sulfur dioxide and soot are 100mg/m3, 50mg/m3 and 20mg/m3 respectively.And han's business is located in the most strict requirements of eight cities along the river."As a result, biomass boilers were later required to follow the same standards."Although this is still far from the "ultra-low emissions" of nitrogen oxides of 50mg/m3, sulphur dioxide of 35mg/m3 and smoke of 5mg/m3, it is a great challenge for biomass boilers.In some provinces, such as zhejiang and shandong, it is harder for biomass companies to discriminate against coal for "ultra-low emissions".So what are the technical difficulties?

Han told reporters that the most difficult part of the standard is the treatment of nitrogen oxides.Professional committee of the China association of circular economy of renewable energy, vice secretary general Wang Weiquan pointed out that at present, the denitration links two of the most mainstream technology is selective catalytic reduction (SCR), and the selective catalytic reduction (SNCR).Small devices can directly oxidize and pressurize the lye to absorb it, in theory reducing nitrogen oxide emissions and even meeting "ultra-low emissions" standards.

But in practice, Han Mou said: "in the biomass boiler flue gas containing alkali metal, heavy metal, etc., using selective catalytic reduction denitration, easy cause catalyst poisoning or even failure, reducing agent can cause in heating surface at the same corrosion and plugging, strict in temperature window, temperature fluctuations can cause the denitration efficiency is low, cannot meet the requirements of super clean emissions."

In addition to technical factors, Wang Weiquan also said that in terms of equipment, "the current national biomass fuel heating scale is still small, and the current domestic denitration equipment are mostly for large coal-fired power plant, the size difference is too big, the cost to bionass enterprise is relatively difficult to bear".

It's hard to make a profit on the standard emissions?

Faced with the embarrassing situation of technology and equipment, the national biomass fuel enterprises have to take measures based on the pressure of environmental protection.

It is understood that in order to reach the environmental protection standard of value of "special", Han Mou three of its existing steam production capacity of 75 tons/hour of biomass boiler using the "ozone + plasma technology" to manipulate the denitration.

"When after plasma smoke purifier, in high-voltage pulsed electric field, through the water, tiny particles of smoke contains high-voltage pulse corona discharge, oxygen, at room temperature to obtain the balance of high and low temperature plasma, which produces a large number of high energy electron and strong oxidation performance of hydroxyl radicals such as high energy particles.Not only has the flue gas been treated and the flue gas has been purified, but the high energy active particles have greatly enhanced its oxidation performance.Han told reporters that this process provides a good reaction condition for ozone to oxidize nitric oxide, which improves the efficiency of ozone to oxidize nitrogen oxides."The spray nozzle was then used to inject the ozone evenly, and the mixing reaction was completed in a very short time. NO in the flue gas was transformed into high-priced nitrogen oxides into the absorption tower."

Although there are technical routes and corresponding attempts, han pointed out that "biomass boilers are relatively low in automation and the content of pollutants in their exhaust emissions fluctuates.Since June new emissions processing equipment production, increased operating costs about 700000 yuan a month, the original profit space is not large biomass fuel companies, cost burden has reached its limits."

Also, Wang Weiquan tells a reporter, at present, the biomass fuel prices of raw materials is about 800-1000 yuan/ton, biomass fuels are usually made of wood particles suppression and become, and wood particles itself is a kind of leftover material of economic value, so the raw material procurement is market competition, the price is hard to fall.Despite the bigger capacity of the boiler and the higher the earnings, "but 'ultra-low emission standard is reasonable for coal, gas, biomass boiler, direct request' ultra-low emissions is difficult.Technology works in theory, but not economically.Wang weiquan admitted."Due to the combustion characteristics of biomass fuel itself, its boiler capacity is currently about 70 tons per hour at most.For small biomass boilers with a capacity of just one tonne an hour, the "ultra-low emissions" standard is a bit overwhelming.

In addition, because of soot particles from coal discharge after biomass combustion is more fine, still need to add in the boiler exhaust gas treatment plant of bag dust removal equipment, daily change, maintenance equipment will also increase the enterprise cost.

"The 'ultra-low emissions' of biomass fuel boilers is not a technical problem, but an economic one."In the eyes of a biomass, head of the enterprise in the north of China, although its provinces have not yet asked biomass to perform "special", "low carbon", but environmental pressure is mounting."Emission standards should not be 'one-size-fits-all'. They should be based on actual measurement and scientific evaluation and reasonable biomass emission standards."