Beware of "side effects" in the implementation of ultra-low emission technology

The development of emission limits requires consideration of multiple factors

The restrictions on the concentration of pollutants specified by the relevant departments, after the key areas, places and power companies (or groups), there are further restrictions, such as the concentration of solid particulate matter discharge from 10mg / m3 requirements to less than 5mg / m3, individual On this basis, the company stipulates a target of less than 3mg/m3 or even 1mg/m3, ignoring the plant's own equipment conditions and the long-term, stability and economy of the ultra-low-emission equipment, and even the low concentration of flue gas solid particles. A strange phenomenon of ambient air particulate concentration at a certain time.

If the concentration of solid particulate matter in the exhaust gas is too low, the range of equipment for selecting ultra-low emission retrofit technology will be relatively narrow, and the transformation cost and operating cost will be greatly improved. In theory, for a 300 MW unit, the amount of solid particulate matter per hour is reduced by a few kilograms at full load, but the coal, water, steam, electricity, etc. consumed for this purpose, if these consumptions are converted into coal, reduce emissions. The goal has not been achieved, and only the beautiful value of less than 5mg/m3 is obtained.

Equipment selection cannot be "one size fits all"

For the selection of ultra-low emission technology routes and equipment, some power companies (or groups) have a "one size fits all" phenomenon. The actual situation of the power plant's geographical location, climatic conditions, boiler form, coal quality, and flue gas conditions are different. If the same technical route and equipment are adopted, the actual operation will not achieve the expected effect, and the power company will appear. Negative devices are used in a lot of other power companies. There has also been a problem of choosing such a technology at a certain time, and another technical route in the next stage, that is, there is no deep understanding of the adaptability of ultra-low emission equipment.

Now select the quality, material selection, design maturity and efficacy of ultra-low equipment to further confirm the operation effect with time, such as the leakage of low temperature economizer into the low temperature or low temperature electrostatic precipitator; the interior of the electrostatic precipitator The slabs and corrosion of the component plates are severe, and the efficient, safe and stable operation of the electrostatic precipitator is greatly reduced, and needs to be continuously improved in the future selection.

The technical route and equipment selection for collaborative dust removal are the most important and most difficult in the whole ultra-low emission transformation. Some cooperative processing equipments have mutual constraints and conditional selection, such as low temperature (low temperature). The high sulfur content, high ash content and high moisture flue gas condition of the dust collector have adverse effects on the low temperature (low temperature) dust collector; for example, the use of flue gas quenching and tempering cannot cooperate with the low temperature low dust collector technology. Dust removal and burning lignite should avoid using low-temperature economizers and low-temperature economizers to avoid dust removal in conjunction with electric bag (bag type) dust collectors.

Problems in the operation of the system and equipment

As a refined equipment, the ultra-low emission device has strict operation and maintenance management requirements, and discovers new problems from the ultra-clean emission equipment that has been operated: In the case of synergistic dust removal equipment , the pole and pole of the low-temperature (low-low temperature) dust collector are used. The corrosion and scale of the plate and the inner wall are gradually exposed, especially the problem that the temperature of the flue gas is below 100 degrees Celsius and the old dust collector is prominent, and the low temperature (or low temperature economizer) leaks seriously. The influence also causes uneven distribution of the airflow at the inlet of the electrostatic precipitator, which affects the efficiency of the electrostatic precipitator. Due to the change of dust properties caused by the input of low-temperature economizer, dry ash removal is also affected, and ash blocking occurs.

In the ultra-clean emission modification of denitrification SCR, due to the full-load denitration and the reactor flow field did not meet the design requirements, the design parameters of the new catalyst and the original catalyst did not meet the overall performance requirements, and the ammonia slip concentration and sulfur trioxide conversion rate were high. , causing blockage, scaling and corrosion of downstream equipment.

In the ultra-clean emission modification of the desulfurization system, due to problems such as limestone quality and wastewater discharge, the absorption tower slurry poisoning and foaming are more, which affects the performance of the high-efficiency dust removal and defogging mist eliminator for removing solid particles.

Due to the current large-scale use of low-temperature economizer technology and wet electrostatic precipitator, the current load ratio of the unit is relatively low, and the water balance of the desulfurization system cannot be controlled, which increases the difficulty of operation of the desulfurization system.

At present, various new types of high-efficiency dust removal and demisting devices are used, and there is a case where the design value is not reached. In the case where wet electricity is not selected, the control of the solid particle concentration below the design value cannot be guaranteed for a long time.

Performance acceptance after transformation

After the power plant reformed the ultra-clean emission system and equipment, the performance test was urgently carried out just 168 hours after completion. The purpose was to complete the national and local time, and also to enjoy the preferential policies of electricity price subsidies and electricity for ultra-clean emissions. The ultra-clean discharge equipment has not passed the test of time. In principle, the equipment performance test of the major renovation is completed within 3 months to 6 months.

Since the threshold set for the test unit is low, many test units that do not understand the ultra-clean emission system and equipment participate in the test, and the reliability of the test data is reduced.

At present, the ultra-clean emission modification of many coal-fired power plants is carried out by the subordinate units of the power company (group), and the subordinates' test units conduct performance evaluation tests and evaluations, which lacks credibility. Performance test acceptance and evaluation shall be carried out by a third party with power industry and manufacturer's unqualified qualifications for power industry commissioning.

Some local environmental protection departments require that the instruments of the online monitoring system must meet the equivalent straight pipe length required before and after the installation location. Otherwise, it is not subject to acceptance. Some power plants have entered the chimney to increase the straight flue, which increases the system running resistance. Technical problems can be solved by technical means. There is no need to increase operating costs and energy consumption. The increase in energy consumption is an increase in pollution. It is recommended that relevant departments conduct in-depth research on this.

The investment in ultra-clean emission equipment of coal-fired power plants plays a decisive role in the improvement of the current environment. However, we cannot ignore the “side effects” caused by the investment of equipment, and the effect of avoiding the investment of ultra-clean emission equipment is greatly reduced.

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