Wet Desulfurization System Research Articles

SO3 removal rate and emission test of the limestone-gypsum wet desulfurization system for coal-fired power plants

This paper studies the SO3 removal ability of dual tower wet desulfurization (in series) and adopts a combination of on-site flue gas sampling and laboratory condensation control. A dual tower (series) supported boiler is used. The SO3 content in the original and clean flue gas of the dual cycle wet desulfurization device was measured, and the removal rate of SO3 of the device was measured. Desulfurization is calculated on the basis of the influence of unit electrical load, coal sulfur content, and desulfurization (raw material flue gas) inlet particle concentration on removal rate. This paper discusses and analyzes the SO3 and SO3 emission concentrations for SO3 removal rules in desulfurization systems. The results indicate that the total sulfur content of coal is relatively high, and the concentration of SO3 is relatively high. The traditional flue gas and net flue gas content in the dual tower wet desulfurization system (series) is relatively high. When burning sulfur-containing coal, there may be “blue smoke” in the flue gas. When the unit load changes between 182 MW and 350 MW, the SO3 removal rate of dual tower wet desulfurization (in series) is between 46.7% and 65.3%, with a net flue gas SO3 concentration of 16.0 mg/m3∼20.5 mg/m3. Due to equipment layout and other reasons, the SO3 removal rate of the primary tower is lower than that of the secondary tower. The removal rate of SO3 is also affected by the concentration of original smoke particles. Due to the condensation of SO3 on the particles and the dust removal of the adsorption tower, the higher the concentration of raw flue gas particles is, the higher the removal rate is. SO3 will be higher. The study also suggests the SO3 removal ability of double tower (series) and double ring wet desulfurization, which is better adapted to changes in load and coal. The next step is to explore the SO3 removal capacity of the dual tower system by optimizing its operating parameters. In addition, due to the arrangement of a desulfurization system after dust removal, it is impossible to control the SO3 source. Subsequent research can control the production of existing SO3 through coal distribution and combustion control.

Research on Control Method of Wet Desulfurization System for Coal-fired Boiler

In wet flue gas desulfurization technology, the key factor affecting flue gas SO2 absorption is the control of slurry pH value in the absorption tower. However, most of the commonly used pH value control methods have some defects and cannot fully meet the system control requirements. On the basis of the analysis for the problems in the control process, this paper discussed a control strategy based on internal model control algorithm. The system simulation test showed that this control method had good dynamic performance, robustness and anti-interference, which could realize the relatively accurate control of pH value for wet flue gas desulfurization system, and achieve the control goal.

Technical Transformation and Energy saving Analysis of Desulfurization System in Coal-fired Power Plant

Taking a 200 MW coal-fired power plant in North China with a limestone-gypsum wet desulfurization system transformation project as an example, the effect of energy-saving transformation of the desulfurization system was evaluated by analyzing the impact of the transformation on the desulfurization efficiency and main energy-consuming equipment. The practice shows that the desulfurization efficiency is greatly improved and the average energy consumption of the desulfurization system is reduced by 29%, achieving the purpose of improving efficiency and saving energy.

Causes and treatments of foaming and overflow of calcium-based wet desulphurization slurry

During the operation of the calcium-based wet desulfurization system, slurry foaming and overflow are prone to occur, which is not conducive to the safe and stable operation of the desulfurization system. In order to solve the problem of slurry foaming, the main properties of the slurry were tested by taking the wet flue gas desulfurization device of a sintering machine of a steel company as an example. The foaming ability of the liquid is characterized by its foaming height and defoaming time, and the influence of surface active substances, particles and metal ions in the slurry on its foaming ability has been studied through multiple experiments. Combining the foaming mechanism and the desulfurization process, the cause of the slurry foaming is analyzed, and measures are given to prevent and treat the slurry foaming overflow to ensure the normal operation of the absorption tower.

Operation optimization and costs analysis of the wet desulfurization system in an ultra‐supercritical coal‐fired power plants

AbstractWith the increasingly strict requirements on energy saving and environmental protection, the economical, efficient and environment friendly operation of large coal‐fired units are being more and more critical. In light of the technical problems of massive energy consumption and high cost in the operation of the wet desulfurization system in a 1,000 MW ultra‐supercritical boiler, the effects of slurry circulation pump combination, slurry pH and absorption tower liquid level on desulfurization efficiency under different unit loads were tested, and the total operating costs were calculated. The results showed that the power consumption under different conditions could be greatly reduced by changing the combination of slurry circulation pumps. The power cost increases from 1,059.42 to 1,146.99 yuan/hr as the combination of slurry circulation pump changes from AC pump combination to BD pump combination under 1,000 MW, increased by 7.63%. Considering all factors, the combination of BC circulating pump can effectively reduce the power consumption cost and achieve the optimal economical operation under the load of 1,000 and 750 MW. The desulfurization efficiency is in direct proportion to the increase of slurry pH. The optimal pH of slurry under 1,000 MW is in the range of 5.50–5.60, 4.80–4.90 under 750 MW, and 4.50–4.60 under 500 MW. Besides, the absorption tower liquid level has a significant impact on the energy consumption of desulfurization system. With the decrease of the absorption tower liquid level, the power consumption cost of desulfurization system shows a downward trend. To avoid the frequent adjustment of liquid level which may result in safety accidents, the optimal liquid level of absorption tower is maintained at 8.00–9.00 m under different unit loads. The research results can provide significant guidance for the operation optimization and fine management of the desulfurization system of the same type.

Research and engineering practice of catalytic absorption of NO2 by tetrabutylammonium hydrogen sulfate for simultaneous removal of SO2/NOx

Under the pre-oxidation condition, NO can be removed simultaneously with SO2 in the existing wet desulfurization system. NO2 absorption efficiency in the wet desulfurization system is low, and additives need to be added to achieve efficient removal. In this work, a novel additive was used (tetrabutylammonium hydrogen sulfate, THS) for the simultaneous removal of NO2 and SO2. Both lab-scale and pilot-scale experimental systems were employed to study the absorption and removal characteristics of SO2 and NO2, and realize engineering application on a 35 t/h industrial boiler. It has been shown that the NO2 removal efficiency in a traditional wet desulfurization system is less than 20%. Adding THS can stabilize SO32− and improve the NO2 removal efficiency. SO2 can promote the absorption of NO2, but O2 in the flue gas and NO2– in the absorption system can inhibit the removal of NO2. In engineering, THS can increase the NO2 absorption efficiency from 13% to 70%, which has great application potential.

ORP as slurry oxidation index and model modification in wet desulfurization system

ABSTRACT Due to wet desulfurization system lacks effective control indicators for the oxidation process, so the sulfite oxidation in the slurry and the quality of gypsum become unstable. In this paper actual desulfurization system operation data are used to improve the ORP semi-empirical formula obtained in the laboratory. It was concluded that the ORP was mainly affected by the concentration of sulfite and pH during the operation of the actual desulfurization system, the dissolved oxygen was less affected by the small concentration change during operation. It is verified that the model can correct the ORP measurement value by using other conventional measurement data from the power plant. The results can provide theoretical support for adding ORP as a control index to optimize the oxidation process. Implications At present, the main control parameter of wet FGD is pH control, but wet FGD has two main reactions at the same time, one is acid-base reaction, the other is redox, single pH control can not reflect the degree of redox, so it is necessary to introduce another control index to evaluate redox, which is the ORP control proposed in this paper, ORP can reflect the degree of slurry oxidation, avoid the occurrence of excessive oxidation and inadequate oxidation, so that the operation of desulfurization system can be more healthy and stable.

Selection of typical wet desulfurization system and economic analysis of variable load operation for industrial coal-fired boilers

In this paper, the operation costs of wet flue gas desulfurization based on MgO, CaO and CaCO3 under basic, special and ultra-low emission limits are analyzed from the unit price of desulfurizer and electricity price. Guidance about desulfurizer selection in Liaoning Province under different electricity prices and different loads is given. The results show that the desulfurization cost of MgO is greatly affected by the desulfurizer price, while the CaCO3 is more sensitive to the fluctuation of electricity price, and the CaO is between the two. In Liaoning Province, the overall economy of CaCO3 is relatively poor in the whole range of electricity price, while CaO and MgO perform better. The former has obvious advantages at low electricity price, while the latter is preferred at high. With the emission standard becoming stricter, the dominant range of CaO is expanded. When the boiler load changes, the power consumption cost and desulfurizer cost also change accordingly under different emission requirements. When the electricity price of Liaoning Province is 0.8 RMB/kWh, no matter under which emission limit, the operation cost of MgO is always the lowest under the considered loads, followed by CaO, and the economy of CaCO3 is the worst.

Investigation of Ash-Related Issues During Combustion of Maize Straw and Wood Biomass Blends in Lab-Scale Bubbling Fluidized Bed Reactor

Abstract During the combustion of solid fuels, the undesired effects of ash transformation include bed agglomeration, slagging, and fouling processes. In particular, a problematic consequence of bed agglomeration is the defluidization process, resulting from the disappearance of gaseous bubbles that are created behind air distributors. Different solutions can be applied against the agglomeration process. One possible method is to apply some additives that influence the ash behavior, thus inhibiting the agglomeration process. This paper presents the results of investigations into ash-related issues in a laboratory-scale bubbling fluidized bed (BFB) reactor. In particular, the impact of additives (kaolin, halloysite, fly ash, and the residuals from wet desulfurization system (IMOS)) on bed agglomeration was investigated. It was found that the addition of these compounds increased the defluidization time from ∼109 min (without additive) to ∼285 min in the BFB (with the addition of 0.1 g/min of kaolin). The morphology of additive (kaolin and halloysite) transformation after their addition into the combustion chamber was discussed. Another interesting phenomenon is that residuals from the IMOS exhibited the ability to be an additive against the agglomeration process. The defluidization time can be also significantly increased by the simultaneous application of the additive and the control of fluidization air velocity. The procedure of periodical bed moving by impulse primary air feeding against defluidization (PADM) is suggested and discussed. The PADM procedure resulted in a 36% reduction of additive, thus reducing the cost of measures against ash-related issues.

Tributyl phosphate additive enhancing catalytic absorption of NO2 for simultaneous removal of SO2/NOx in wet desulfurization system

Removal of SO2 and NO emissions from coal-fired power plants have always been the focus in coal's utilization industries for which traditional wet desulfurization system hold the potential to achieve simultaneous removal of SO2/NOx. In this work, a novel liquid catalyst (tributyl phosphate, TBP) was investigated for the simultaneous removal of SO2 and NOx in a NO pre-oxidation (ozone oxidation) assisted process. The absorption process and reaction mechanism of SO2 and NO2 were studied in a small-scale experimental system, and the removal efficiency of pollutant and the key parameters were examined in a pilot-scale system. The results show that the removal efficiency of NO2 in traditional wet desulfurization system is only 20–40%; however greatly increases to >90% when TBP is added. Moreover, TBP can enhance the NO2 removal performance in the presence of SO2 due to the formation of TBP–NO2–SO32− complex. Considering the oily nature of TBP that can be easily separated, such addition strategy hold great potential for industrial SO2/NOx simultaneously removal.

210Po concentration in desulfurized waste water of coal-fired power plant

ABSTRACTThe concentration of 210Po in the desulfurized waste water can be affected by the operation of the wet desulfurization system in the coal fired power plant (CFP). However, this correlation ...

Experimental study on the evaporation and chlorine migration of desulfurization wastewater in flue gas.

Wastewater from a limestone-gypsum wet desulfurization system cannot be directly reused or discharged due to its high suspended matter content and complex water composition. Desulfurization wastewater evaporation in flue gas is an effective way to dispose wastewater. Multicomponent soluble chlorine salts exist in the desulfurization wastewater. During the evaporation, chlorine enters into the flue gas due to volatilization, which accelerates the enrichment rate of the Cl- concentration in the desulfurization slurry and leads to an increase in wastewater production. This study explored the chlorine migration of various chlorine salt solutions and typical desulfurization wastewater at high temperature during the evaporation process of concentrated wastewater by a laboratory-scale tube furnace and a pilot-scale system. Results showed that when NaCl-evaporated substance was heated, the chlorine ion hardly volatilized. For the evaporated substances of CaCl2 and MgCl2 solutions, some of the crystal water was lost, and hydrolysis occurred to generate gaseous HCl. NH4Cl was easily sublimed, and the decomposition temperature was lowest. A pilot study on spray evaporation of desulfurization wastewater in flue gas showed that the particle size of the evaporated product increased and the main particle size was within 2.5-10μm with increasing flue gas temperature. Increasing the mass ratio of gas to liquid significantly reduced the particle size of the atomized particles, thereby reducing the average particle size of the evaporated particles. The HCl concentration increased with increasing flue gas temperature. When the flue gas temperature was 350°C, the concentration of HCl was 40ppm, and the escape rate of chlorine in the desulfurization wastewater was approximately 30% using typical wastewater from a limestone-gypsum wet desulfurization system.

Discussion on the cause of scaling in wet desulfurization system of large coal-fired power plants

The flue gas desulfurization method of large coal-fired power plants is generally limestone/gypsum wet method. But many equipments of this wet desulfurization system during daily operation often cause scaling problems. At present, more literature think s this scale is caused by the mixing of desulfurized gypsum and fly ash in flue gas. However, this paper analyzes the scale composition and appearance of several power plants in China, which shows that the scale is not a simple mixture of gypsum and fly ash, and is a smelting reaction of fly ash in a complex environment and forms a hard scale of gypsum/limestone-fly ash gel. This kind of scale will endanger the safe and stable operation of the desulfurization system, specific operational and maintenance recommendations are proposed for reference.

Field tests and optimal operation research of WFGD for a 600MW power plant

In this paper, wet desulfurization system for a certain 600 MW coal-fired power unit was studied. The field tests were conducted on the limestone wet flue gas desulfurization system of a coal-fired unit. The influence of absorber entrance concentration of SO2 at different loads, as well as the absorber slurry pH value under variable numbers of slurry circulating pumps on desulfurization efficiency were tested. The experiment results also drawn that the start and stop effects of circulating pump on the efficiency of desulfurization rate under different load and the relationship of the slurry density and gypsum quality. On the basis of operation cost analysis, overall power consumption of desulfurization system and the emission fee would be reduced. The optimal operation mode of the slurry circulating pump is given, and the pH value and slurry density are determined.

Pilot-scale study on water and latent heat recovery from flue gas using fluorine plastic heat exchangers

Over the years, in order to enhance the thermal efficiency, coal-fired power plants have witnessed great improvements in water and waste heat recovery. This paper aims to investigate the water vapor and latent heat recovery from the low temperature flue gases exiting a limestone-gypsum wet desulfurization system. A pilot-scale testing system mainly composed of a two-stage fluorine plastic heat exchanger (FHE) was built in a 660 MW lignite-fired power plant in northern China. The additional FHE configuration was first developed and used for water and latent heat recovery based on the condensation mechanism of water vapor. Results showed that the FHE can overcome the shortcomings of the conventional metal heat exchanger, especially when flue gas temperature is below the acid dew point. The recovered latent heat accounted for more than 80% of the total heat recovered from low temperature flue gases, and the heat supply of 92 MWth was achieved. The overall heat transfer coefficient of the FHE reached up to 275 W/(m2•K). The water recovery efficiency increased with an increase in cooling water velocity and a decrease in flue gas velocity. The water recovery efficiency higher than 70% was reached when the flue gas velocity was less than 5 m/s and the cooling water velocity was greater than 0.24 m/s. The highest water recovery efficiency of the two-stage FHE was 85%, suggesting that this technology has a greater application potential in all industrial processes. The recovered water mass from the flue gas by condensation was nearly equal to, or even exceeded, the equivalent mass of supplemental water for the desulfurization system. The good water recovery performance of the FHE device implied that zero water consumption of the desulfurization system could be achieved, which is of great significance for power plants, especially in water scarce regions. This technology will offer an innovative and feasible solution to resolve the issue of water and heat recovery in the highly corrosive conditions.

Discussion and Analysis on Effect of Hot Secondary Air Governance Gypsum Rain on the Power Plant Unit

For gypsum rain phenomenon in limestone-gypsum wet desulfurization system. This article made programme that has used unit existing equipment allowance. Extracted hot secondary air to heat purified flue gas to eliminate "gypsum rain". This programme is implemented which makes temperature of purified flue gas rising to 70 °C. That almost eliminate "gypsum rain" phenomenon. While temperature of boiler exhaust gas declined, and temperature of hot air reduced, and boiler thermal efficiency declined, unit of power coal consumption rosed. Comparing to other programmes, this programme has a larger advantage in technology, economic, and security aspects.