Advantages and disadvantages of VOCs waste gas as auxiliary gas for coal-fired boilers

The severe air pollution situation has forced the government, environmental protection supervision departments, enterprises, and the public to have a clearer understanding, and basically formed a consensus, that is, waste gas treatment is imperative, not a question of whether to do it, but how to do it. , How to do a good job.VOCs are important precursors for the production of nitrogen oxides and ozone through photochemical action. VOCs waste gas is a deep water area for waste gas treatment, which is much more difficult than flue gas treatment and odor control.

The relative lag of technical policies, technical guidelines, regulations, and standards in the treatment of VOCs waste gas not only makes it difficult for enterprises to choose a technical route, but also leads to mixed good and bad environmental protection engineering companies, a large number of bad money driving out good money, repeated prohibitions on winning bids at low prices, and more and more garbage projects. More and more, secondary investment has almost become the norm. At the same time, it has brought problems such as difficulty in law enforcement by environmental protection supervision departments and difficulty in judging the merits of projects.

The following is an analysis of the advantages and disadvantages of using VOCs waste gas as auxiliary gas for coal-fired boilers.

Many enterprises have the problem of low concentration of VOCs exhaust gas and large emissions, such as drying exhaust gas generated during the drying process of solid products, spraying exhaust gas and drying exhaust gas in the spraying industry, and volatile exhaust gas from circuit printing boards, etc. The concentration of these VOCs exhaust gas is only per cubic meter The amount of waste gas is tens or hundreds of milligrams per hour, and the amount of waste gas is often tens of thousands, hundreds of thousands, or millions of cubic meters per hour. Enterprises believe that these waste gas, no matter what kind of treatment technology is adopted, the investment is relatively large.

In this case, companies with coal-fired boilers naturally thought of passing these waste gases directly into the boiler as auxiliary gas.It is true that there is no current regulation that these waste gases cannot be treated in this way, not to mention that these waste gases may contribute some basic calorific value and reaction heat. More importantly, or what enterprises value more, do not need to invest too much money for the time being.

However, according to the author, there are still certain risks in doing so. The analysis is as follows:

1. Security risks.Because there are no corresponding safety measures, or the safety measures are insufficiently equipped, such as combustible gas concentration detectors, safety interlocks, supplementary fresh air measures, emergency shut-off valves, bypass systems, etc., when the concentration of exhaust gas exceeds the explosion limit or the high-concentration air mass comes over, Flash explosion accidents are prone to occur; the risk is higher if the boiler flames out or the boiler production is not synchronized with the exhaust gas emission.

2. Compliance risk.VOCs waste gas treatment far exceeds that of flue gas treatment and odor control. Based on this, the government has begun to vigorously promote "one factory, one policy"; also because of this, many environmental protection engineering companies engaged in flue gas treatment and odor control. After The complexity of entering the VOCs governance market, most of them are "Laughing in, crying out".When the exhaust gas is fed into the boiler as auxiliary gas, there are not enough measures to ensure the treatment effect, and the exhaust gas cannot be fully burned, especially when the molecular structure is relatively stable, the molecular weight is relatively large, or the instantaneous concentration is relatively high, the compliance is even more uncontrollable.

3. Policy risk.Because VOCs waste gas is passed into the boiler as auxiliary gas and is discharged through the chimney, the current flue gas detection items are only sulfur dioxide, nitrogen oxides, particulate matter, etc., and do not detect VOCs concentration, VOCs removal rate, odor concentration and characteristic pollutants.Once the corresponding regulations are implemented, there will be two results: ( ) The practice of passing 1recognized , but the detection related to VOCs waste gas into the boiler as auxiliary gas will be VOCs will be increased . This detection needs to consider the air dilution factor and apply the concept of reference oxygen. It is very difficult to meet the standard; ( 2) It is considered that the introduction of waste gas into the boiler as auxiliary gas is not a waste gas treatment technology, and accordingly this method is not allowed.

4. Technical risk.The design of the boiler is approved by the boiler inspection institute. If waste gas is introduced, the calorific value will change, not only the pollutants cannot be cured, but also may affect the normal combustion of the boiler.

5. Legal risks.Exhaust gas is fed into the boiler as auxiliary gas. In the event of a safety accident or other problems, the responsibility lies with the enterprise, because there is no corresponding design basis.

The author believes that there are still many options for VOCs waste gas treatment technology, such as absorption method, adsorption method, condensation method, membrane method, thermal incineration technology, catalytic oxidation technology, etc. These technologies are also relatively mature, as long as the idea of ​​gradient coupling technology is followed. , The correct selection of the process route, the investment in waste gas treatment is still acceptable.

The author suggests that VOCs waste gas cannot be treated as auxiliary gas into the boiler, but targeted control measures should be taken, so as to achieve the right medicine, cure the disease, and avoid safety risks, compliance risks, policy risks, technical risks, and legal risks. And so on, solve the worries of the enterprise, let the enterprise focus on its core business.