Industry new

Technical scheme of pneumatic pinch valve in power plant flue gas dedusting and desulfurization

At present, the flue gas dedusting and desulfurization emitted by coal-fired power plants are mostly designed and operated separately, and the integrated design is less. Dust-removing equipment mostly uses electrostatic precipitators and bag filters. These facilities have high dust removal efficiency, but the desulfurization effect is poor, and sulfur dioxide emissions are not up to standard. The desulfurization process mainly adopts the wet desulfurization technology of double alkali method and ammonia water method. The limestone-gypsum wet desulfurization process is the most widely used and mature technology in the world, but the limestone-gypsum desulfurization technology project has large investment and high running cost. Equipment and piping systems are prone to wear and blockage and are not suitable for small to medium sized boilers and kilns.

First, the importance of dust removal and desulfurization of power plant flue gas

Environmental protection is a basic national policy of China. With the continuous improvement of China's environmental protection laws and regulations and the acceleration of technological advancement in various industries, the people's call for environmental protection is getting higher and higher. The continuous development of China's power plant industry and the growth of GDP. China is facing increasing environmental pressures, and environmental governance can't keep up. China will repeat the old road of industrialization that has been passed by the western developed countries, and the state is increasingly strengthening the environment. . The environmental protection efforts can not keep up, it will cause great damage to the surrounding ecology. The use of clean coal chemical technology, the development of circular economy, the maximum realization of resource recycling and reuse, turning waste into treasure is the fundamental reason for enterprises to increase efficiency. This is consistent with the development of a circular economy model strongly advocated by the state.

Second, wet dust removal and desulfurization - body design

The integration of wet dust removal and desulfurization mainly consists of dust removal and desulfurization system, anti-condensation system, water supply system, circulation and sewage system, lime slurry preparation system and control system.

The basic principle of dust removal in flue gas dedusting and desulfurization system is to use a two-stage dust removal device to remove dust pollutants from the flue gas. The first-stage dust removal uses the downward movement of the water film in the dust removal and desulfurization tower to collide with the upwardly moving dust-containing flue gas, intercept and agglomerate to remove the dust; the secondary dust removal is formed by the small centrifugal nozzle of the venturi tube. The water film and the dusty fine droplets adiabatically expand to form large droplets for dust removal. The flue gas flowing out of the venturi tube enters the existing trapper. The trapper not only removes part of the moisture in the flue gas, but also dedusts the remaining ash-containing water droplets in the flue gas. The dust removal efficiency of the entire dedusting system It is 99.6%.

The anti-condensation system is set to prevent condensation in the induced draft fan when the ambient temperature in the winter is low and the system smoke temperature is low. The system consists of two parts. One is to take out the bypass flue from the flue of the boiler tail. After the ceramic multi-tube dust collector, part of the flue gas is introduced into the outlet of the trap and the inlet flue of the induced draft fan. The second is from the air. The preheater draws hot air directly to the inlet flue of the induced draft fan to increase the flue gas temperature of the induced draft fan and prevent condensation of the flue gas. These two measures will be selected according to changes in external conditions such as ambient temperature.

The hydration system is a system for replenishing the whole system with new water. The new water is supplied by the dust removal pump in the plant, and is added to the venturi nozzle, the lower part of the dust removal and desulfurization tower and the digesting tank. The dust water after washing and dusting enters the bottom of the desulfurization and dedusting tower to participate. A grey water cycle for dust removal. The circulating water system includes a primary sedimentation tank, a secondary sedimentation tank, a circulating water pump and a pipeline, and the ash water collected at the bottom of the trap and the venturi and the purified water in the primary sedimentation tank are finally introduced into the secondary sedimentation tank. The purified water after the sedimentation of the secondary sedimentation tank is returned to the dust removal and desulfurization tower through the circulation pump to dedust and desulfurize the flue gas. The first settling tank is gravity-drained through the pinch valve at the bottom, and the mud settled at the bottom of the secondary sedimentation tank is mud-treated. The pump is discharged into the ash ditch.

The desulfurization technology in the integrated system of wet dust removal and desulfurization is a simple desulfurization technology developed based on the current mature wet desulfurization technology principle. The technology uses quicklime or slaked lime as a desulfurizing product, and is added into a dedusting circulating solution by digesting and preparing a lime slurry, and removing sulfur dioxide in the flue gas while removing dust. The system consists of a system of transportation and storage of desulfurizing product, digestion of desulfurizer, and transportation of lime slurry.

The control system of the wet dust removal and desulfurization integrated system adopts advanced development software and equipment, mainly controlling the water supply amount of the dust removal system, the liquid level of the dust removal and desulfurization tower, the pH value of the circulating water of the desulfurization system, thereby ensuring the desulfurization efficiency; Comprehensive control of all aspects of operation and operation and system start-stop, accident judgment and adjustment. Compared with the use of electric dust removal and wet desulfurization technology, the total investment of this set of wet dust removal and desulfurization integrated system is only about 1,10 of the former, which is very important for large and medium-sized units with long life and low residual value. Good economic and technological advantages.

Third, the new development of the technology

At present, there are dozens of desulfurization processes used in coal-fired or oil-fired power plants around the world. According to the desulfurization process, the parts in the production can be divided into three categories: pre-burning (before combustion) desulfurization, furnace (in combustion) desulfurization and post-furnace (post-combustion) desulfurization. Among the commercial desulfurization technologies, the main method still used is flue gas desulfurization. Among them, limestone-lime wet desulfurization technology dominates.

The flue gas wet desulfurization technology has a high desulfurization efficiency, but it occupies a large area and has a high investment. Therefore, it is not attractive for the transformation of old units and projects that require investment reduction. In the 1970s, a power company in the eastern United States used a desulfurization technology with a desulfurization efficiency of only 25% in one of its operating units. This technology combined with raw coal cleaning technology enabled the unit to meet The new environmental emission standards require that due to the low investment in this technology, it has aroused people's enthusiasm for the development of research on low-investment desulfurization technology. At the same time, the US Environmental Protection Agency has continued to fund some industrial trials to develop desulfurization technologies for small units, old units, and low investment costs.

In the initial stage of development and research, a technique of desulfurizing the furnace by spraying calcium into the furnace through a multi-stage low NOx burner was adopted. A series of studies were carried out by spraying limestone jets into the furnace in different temperature zones of the furnace. It is proved that this desulfurization technology can achieve moderate desulfurization efficiency. After a series of studies, B&w conducted an industrial test on a 105Mw unit boiler called the “Limestone Jet Multi-Class Burner Demonstration Project (uMB)”. This is the prototype of the above-mentioned furnace calcium desulfurization technology. The successful trial of the uMB demonstration project and the subsequent implementation of the uMB expansion demonstration project funded by the US Department of Energy have led to the development and improvement of this technology and its application in industry.

In the development and research process of calcium injection technology in the furnace, a series of other related technologies have been carried out, some of which have been used again in the development of desulfurization technology, and several other absorbents have been developed. Jet desulfurization technology. These technologies include: calcium flue desulfurization technology in the tail flue, calcium spray-spray drying desulfurization technology (uDs) in the furnace, and sO:, N0x, fly ash comprehensive removal technology (sNRB). At present, these three technologies are still in the experimental research stage, and they all have broad market potential because they all have the advantage of low investment cost.

Due to the many years of commercial operation experience of limestone (lime) spray drying desulfurization technology, the investment operation cost is relatively clear. Although there is no detailed comparative analysis with the wet desulfurization system, the industry generally believes that the cost of the spray drying desulfurization system is about Between 80% and 90% of the wet desulfurization system.

Since the calcium spray drying and desulfurization system and the sNRB system in the furnace are still in the stage of modeling test, it is not yet possible to know the cost and cost of commercialization in the future. According to the data currently available, it is estimated that the investment cost of the calcium spray spray drying desulfurization system in the furnace is equivalent to that of the spray drying desulfurization system, and the annual operating cost is lower than that of the spray drying desulfurization system. The economics of the sNRB system is currently the most uncertain. Because the technology combines the functions of desulfurization, denitrification and dust removal, it is optimistic to estimate that, under the premise of achieving the same effect, it is better than desulfurization and denitrification separately. The economy of dust removal is high.

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