Semi-dry Desulfurization Process with In Situ Supported Sorbent

Article pubs.acs.org/EF

Semidry Desulfurization Process with In Situ Supported Sorbent Preparation Dong Xie, Haiming Wang, Dongwu Chang, and Changfu You* Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Thermal Engineering, Tsinghua University, Beijing 100084, China ABSTRACT: Semidry desulfurization process with in situ supported sorbent preparation was studied. The effects of bed inventory, slurry sprayer height above the distributor, and slurry spray method on desulfurization efficiency were tested. The results showed that desulfurization efficiency for 28 kg of bed inventory could reach 98.84% for Ca/S molar ratio of 2.5. This result was approximately seven times higher than the result without bed material because ultrafine Ca(OH)2 particles in the lime slurry adhered to the bed material surface and formed the supported sorbent. A lower slurry sprayer height and countercurrent slurry spray could reach an even higher desulfurization efficiency. The desulfurization efficiency of this proposed process was approximately 30−40% higher than that of the supported sorbent prepared by the original hydration and drying method at high Ca/S molar ratio due to better contact efficiency between water and sorbent particles. studies.21,22 In this process, CaO and circulating ash were mixed with water in a stirring tank at ambient temperature for approximately 2 h and then the mixture was dried at 150 °C for approximately 1 h. The hydration temperature and time are both much lower than previous preparation processes; as such, they are more suitable for industrial application. Because ultrafine Ca(OH)2 particles adhere to fly ash surface, the desulfurization performance of supported sorbent is much better than industrial sorbent.23 At ambient temperature, there are little highly active pozzolanic reaction products.24 Hence, the reason for the improved sorbent utilization of the supported sorbent is not the same as the previous ordinary lime/fly ash sorbent. Here, preparing supported sorbent using CaO and fly ash causes lumps of CaO to decompose into ultrafine Ca(OH)2 particles in water because the reaction of CaO and water releases a large amount of heat. The average diameter of these Ca(OH)2 particles is approximately 7 μm.24 During the drying process, the water evaporates and then Ca(OH)2 particles adhere to the fly ash surface. In the CFB reactor, adhering ultrafine Ca(OH)2 particles are captured by the cyclone separator before they detach from the fly ash surface. Adhering ultrafine Ca(OH)2 particles have longer residence time than nonadhering ultrafine Ca(OH)2 particles, which results in high sorbent utilization of the supported sorbent. The supported sorbent preparation process is an improvement over the previous ordinary lime/fly ash sorbent preparation process; however, it is still too difficult for actual industrial application because the drying of the mixing slurry is energy-intensive and the overall preparing process is complicated. So improvements are essential for the application of the supported sorbent in an actual semidry desulfurization system. Due to its intense mass and heat transfer, fluidized beds are widely used for spray granulation from solutions, suspensions,

1. INTRODUCTION Sulfur dioxide (SO2) emissions from coal-fired electric power plants are recognized as contributors to serious environmental problems, including acid rain and respiratory disease in humans.1,2 There are many flue gas desulfurization (FGD) processes to reduce SO2 emissions.3−5The wet FGD process using limestone slurry as the absorbent is widely used due to its good operation stability and high desulfurization efficiency. The advanced wet method is capable of reaching high SO2 removal efficiency of 92−98%.6,7 However, the capital cost and operation expenses are relatively high, especially for smallcapacity coal combustion power plants. In addition, the wet FGD process consumes a significant volume of water, which is not feasible in water-lacking areas.8,9 The treatment of wastewater is also a serious problem for the wet FGD process. The semidry FGD process is an attractive alternative owing to its low capital cost, small space occupation, significantly less water consumption, and no wastewater treatment, which make it suitable for small-capacity coal combustion power plants and old unit desulfurization retrofits.10,11 Nevertheless, low sorbent utilization and poor operation stability make it difficult for industry application. Numerous studies have attempted to improve sorbent utilization for semidry FGD processes.12−18 Most of these studies focus on enhancing sorbent activity using a hydration mixture of lime and Si-containing waste, such as fly ash, rice husk ash, and clay.15−18 The Si-containing waste reacts with lime in the presence of water, which is known as a pozzolanic reaction. High sorbent reactivity mainly results from the large specific surface area of these pozzolanic reaction products.17 High hydration temperature and long hydration time are essential for the formation of the pozzolanic reaction products.19,20 These difficult preparation conditions, which increase the capital cost and operation expenses of the semidry desulfurization process, make it difficult to be used in an actual desulfurization process. A low-cost supported sorbent has been previously prepared using lumps of CaO and fly ash as raw material in our previous © XXXX American Chemical Society

Received: December 16, 2016 Revised: March 2, 2017 Published: March 17, 2017 A

DOI: 10.1021/acs.energyfuels.6b03354 Energy Fuels XXXX, XXX, XXX−XXX

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Energy & Fuels

Figure 1. Pilot-scale CFB reactor system. SO2 mixing chamber, which contained a designated concentration of SO2. The gas temperature was modified by the air cooler. The riser was 6 m high, and the diameter was 0.305 m. Flue gas entered the bed through a distributor to make the bed material fluidize. The lime slurry was injected into the bed by an air atomizing nozzle above the distributor. When flue gas passed though the cyclone separator, coarse bed material carried by the flue gas was captured by the cyclone separator and then sent back to the main bed. Relatively fine particles escaped from the cyclone separator. In order to enable a comparison of the desulfurization performance with the proposed desulfurization process, the supported sorbent was prepared using the original hydration and drying method. Dry supported sorbent was fed into the main bed through a sorbent feeder, and the slurry sprayer above was used for spraying water. The sorbent feeder was 1.5 m above the distributor. Lime slurry was prepared from water and lumps of lime at a mass ratio of 4.25. The size of the lumps of lime was approximately 2 cm. Lumps of lime benefited production of micro-Ca(OH)2 particles from the original lime.24 Large particles in the slurry were filtered out through a 0.1 mm standard screen to avoid nozzle blocking. The mass ratio of water and Ca(OH)2 in the slurry was about 3.0−3.8 after filtering. The lime was purchased from the Beijing Shougang Building Material Chemical Factory. Silica sand was obtained from the Donghai County Hongda Quartz Material Co.; it was then used as bed material. The supported sorbent was made from silica sand and lumps of lime at mass ratio of 2.0 through hydration and drying method. Lumps of lime and silica sand were mixed with water in a stirring tank for approximately 2 h at ambient temperature. After hydration, the slurry was placed on a vacuum suction filter for water removal; the remaining solid was further dried at 150 °C for approximately 1 h. The resulting dried cake was pulverized into powder with a diameter smaller than 2 mm and then sealed in a bottle before the desulfurization test. For the detailed process one could refer to Zhang et al.24 There were seven SBP800 pressure sensors (range, 0−2 MPa; accuracy, ±0.2%) and eight PT100 temperature sensors (range, 0−200 °C; accuracy, ±0.3 °C) along the riser height to measure flue gas pressure and temperature. The local solid volume fraction near the sprayer was measured by PV-6D optical fiber that was developed by the Institute of Process Engineering, Chinese Academy of Sciences. The SO2 and O2 concentrations at the inlet and outlet of the riser were measured by a PS3400 gas analyzer (SO2 concentration range, 0−5000

and melts in various industries, including pharmaceutical and food processing, waste disposal, and agriculture production.25,26 In these processes, solid-containing liquid is continuously sprayed into the fluidized bed by means of an atomizing nozzle. The hot gas evaporates the solvent, leaving the solute adhering to the bed material surface. The structure of microencapsulation produced by this method is similar to the structure of supported sorbent. Therefore, a viable method for preparing the supported sorbent is the use of lime slurry spray granulation in a CFB reactor. The CFB reactors are also suitable for the supported sorbent to realize high sorbent utilization in actual FGD industrial applications due to the long residence time of the sorbent and intense gas−solid interaction.21 Hence, flue gas desulfurization in the CFB reactor with in situ supported sorbent preparation through the lime slurry spray granulation method may facilitate improvements for the commercial application of supported sorbents in actual semidry desulfurization systems. This study investigated a lime slurry spray semidry FGD process with in situ preparation of supported sorbent at a temperature of approximately 110−150 °C in a pilot-scale CFB experimental facility. The effects of bed inventory, slurry sprayer height above the distributor and slurry spray method on desulfurization efficiency were tested. To evaluate the desulfurization performance of this proposed semidry FGD process, the desulfurization characteristic of supported sorbent prepared by the original hydration and drying method was also tested on the pilot-scale CFB experimental facility.

2. EXPERIMENTAL SECTION Shown in Figure 1 was the pilot-scale CFB experimental facility. It was separated into two subsystems: flue gas generation subsystem and CFB reactor subsystem. The main parts of flue gas generation subsystem were a fan and oil burner. The CFB reactor subsystem consisted of a riser, a cyclone separator, sorbent feed, and a slurry sprayer. The oil burner produced hot air at approximately 300 N m3/ h.Simulated flue gas was obtained by mixing hot air and SO2 in the B


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Energy & Fuels ppm; O2 concentration range, 0−21%; accuracy, ±1%). Inlet and outlet SO2 concentrations were used to calculate the desulfurization efficiency (accounting for system air leakage) when the outlet SO2 concentration became stable. Experiment time for each experimental condition was about 40 min. The chemical compositions of the original lime, silica sand, and postreaction silica sand were measured by X-ray fluorescence (XRF). The particle sizes of silica sand and supported sorbent were measured by a laser diffraction instrument (Malvern Mastersizer 2000). Surface morphology was studied by a scanning electron microscope (SEM), and surface chemical element composition was measured by energy dispersive spectrometer (EDS).

3. RESULTS AND DISCUSSION 3.1. Physical and Chemical Properties. Table 1 lists the chemical composition of the original lime and silica sand

Figure 3. Effect of bed inventory on desulfurization efficiency.

Table 1. Chemical Composition Analysis different bed inventories. The experiments were conducted at the following conditions: Ca/S molar ratio of 0.6−2.5; bed superficial velocity of U = 1.5 m/s; average bed temperature of T = 110−150 °C; inlet SO2 concentration of CSO2 = 1500− 2000 ppm; slurry sprayer height above the distributor of h = 0.1 m; mass ratio of water and Ca(OH)2 at approximately 3.0−3.8 in the lime slurry. Figure 3 shows that the desulfurization efficiency of lime slurry spray without bed material was relatively low. The desulfurization efficiency was 4.80−15.7% when Ca/S molar ratio was 1.24−2.30. The calcium conversion rate was approximately 3.87−6.81% because the Ca(OH)2 particles in the lime slurry uniformly distributed at approximately 7 μm.24 The overall separation efficiency of the cyclone separator was higher than 95%, but the separation efficiency for ultrafine Ca(OH)2 particles was lower than 8%.21Hence, the majority of Ca(OH)2 particles in the lime slurry were carried out of the CFB reactor by the flue gas before reacting with the SO2. The residence time of Ca(OH)2 particles was short, which resulted in a low calcium conversion rate. As the bed inventory increased to 14 kg, the desulfurization efficiency was 6.0−16.5% when the Ca/S molar ratio was 1.03−2.06. It was slightly higher than that without bed material because a few of the ultrafine Ca(OH)2 particles in the lime slurry adhered to the bed material surface during the contact of slurry droplets and bed material. These adhering Ca(OH)2 particles could be captured by the cyclone separator and sent back to the main bed multiple times before they detached from the bed material. Adhering ultrafine Ca(OH)2 particles have a longer residence time than nonadhering ultrafine Ca(OH)2 particles, leading to a higher desulfurization efficiency than the result without bed material. The calcium conversion rate was still less than 8% because the local solid volume fraction near the sprayer was only 0.1, which led to low adhesion efficiency of ultrafine Ca(OH)2 particles on the bed material surface. Most of the ultrafine Ca(OH)2 particles in the lime slurry were carried out before they could adhere to the bed material surface, which resulted in the low calcium conversion rate. The desulfurization efficiency was 20.9−46.1% as the Ca/S molar ratio was 0.85− 1.92, with the bed inventory increasing to 18 kg. The calcium conversion rate was approximately 24.01−26.48%, which was about 3.5 times higher than that of the 14 kg of bed inventory. The local solid volume fraction near the sprayer was approximately 0.19, which was higher than that of the 14 kg of bed inventory. A higher local solid volume fraction led to a higher adhesion efficiency of Ca(OH)2 particles on the bed

content (%) lime silica sand

SiO2

Al2O3

CaO

MgO

Fe2O3

K2O

0.48 98.24

0.17 0.44

92.21 0.12

0.64 0.07

0.05 0.11

0.02 0.02

measured by XRF. The CaO content of lime is 92.21%. The effect of the other impurities, such as MgO, on the desulfurization efficiency is ignored. Figure 2 shows the particle size distribution of the original silica sand and the supported sorbents prepared by the original

Figure 2. Particle size distribution of silica sand and supported sorbent.

hydration and drying method. The average particle diameter of the original silica sand is approximately 243.76 μm, and the average particle diameter of the supported sorbent is approximately 309.89 μm due to the adhesion of ultrafine Ca(OH)2 particles on the silica sand surface. There are approximately 10% volume fraction particles in the supported sorbent with diameters ranging from 1 to 10 μm, which indicates that some Ca(OH)2 particles have not adhered to the silica sand surface during the original supported sorbent preparation process. 3.2. Desulfurization Performance in CFB Reactor. 3.2.1. Effect of Bed Inventory. Bed inventory is a very important operation parameter for CFB reactor because it determines the pressure drop. 27 Figure 3 shows the desulfurization efficiency for the lime slurry spray semidry desulfurization process with countercurrent slurry spray for C


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Energy & Fuels material surface and also higher calcium conversion rate.28,29 The desulfurization efficiency was 23.95−98.84% when the Ca/ S molar ratio was 0.60−2.50, with the bed inventory increasing to 28 kg. The calcium conversion rate was approximately 35.16−39.54% because of the high local solid volume fraction near the sprayer, which was beneficial to the adhesion of Ca(OH)2 particles. Figure 4 shows typical SEM micrographs of the original bed material and the postreaction bed material. The surface of the

chemical composition analysis of the silica sand by XRF. After the desulfurization test, the content of Ca and S increased to 46.62% and 27.08%, respectively, with the content of Si declining to 2.38%. This indicated that the surface of the bed material was covered with particles that contained high Ca and S content. These particles were ultrafine Ca(OH)2 particles in the lime slurry that adhered to the bed material surface and the product of these Ca(OH)2 particles reacting with SO2. The chemical composition of the postreaction bed material was measured by XRF (Table 3). The mole ratio of S and Ca in the postreaction bed material was approximately 0.81, which indicated that the calcium conversion rate of adhering Ca(OH) 2 particles was approximately 81%. This was approximately 16 times higher than that of the nonadhering Ca(OH)2 particles. The overall calcium conversion rate of the 28 kg of bed inventory was approximately 35.16−39.54%, which was half of the calcium conversion rate of the adhering Ca(OH)2 particles. This was mainly due to the large number of Ca(OH)2 particles in the lime slurry that still did not adhere to the bed material surface and the fact that the calcium conversion rate of these nonadhering Ca(OH)2 particles was relatively low. Although high bed inventory led to high desulfurization efficiency, it brought some problems. One of the most important was that high bed inventory caused a high pressure drop. In our experiment, when bed inventory was 14 kg, the pressure drop was only 500 Pa. When bed inventory increased to 28 kg, the pressure drop increased to 2500 Pa. High pressure drop resulted in a high operation cost of the desulfurization system. So there was an optimal bed inventory between zero and the maximum bed inventory, which was a trade-off between desulfurization efficiency and pressure drop. 3.2.2. Effect of Slurry Sprayer Height above the Distributor. The position of the slurry sprayer is an important parameter for achieving high adhesion efficiency and avoiding aggregation.30Figure 5 shows the effect of the slurry sprayer height above the distributor on the desulfurization efficiency with a 28 kg bed inventory and countercurrent slurry spray. When the Ca/S molar ratio was 0.9−2.0, the desulfurization efficiency was 18.7−54.3%, with the calcium conversion rate being 20.8−27.2% for h = 0.9 m. After lowering the slurry sprayer height to 0.5 m, the desulfurization efficiency was 34.7− 91.9% as the Ca/S molar ratio was 1.2−2.7. The calcium conversion rate was 28.9−34.0%, which was approximately 8% higher than that of h = 0.9 m. In the CFB reactor, the solid volume fraction decreased as the height increased.31 The local solid volume fraction near the sprayer at h = 0.5 m was higher than that at h = 0.9 m. This resulted in higher adhesion efficiency of ultrafine Ca(OH)2 particles on the bed material surface. As the slurry spray height dropped to 0.1 m, the calcium conversion rate was approximately 35.2−39.9%, which was approximately 6% higher than that of h = 0.5 m. The results showed that when the slurry sprayer height above the distributor was lower, then the calcium conversion rate was higher. However, a low slurry sprayer height might cause aggregation in the CFB reactor, as observed in the experimental height of h = 0.1 m.30The formation of large agglomerates could cause defluidization, which would adversely affect system stability. Therefore, when choosing the optimum slurry sprayer location, there should be a trade-off between a high calcium conversion rate and the system stability. 3.2.3. Effect of Slurry Spray Method. Co-current slurry spray is widely used in industry application because counter-

Figure 4. SEM micrographs for bed material: (a) original; (b) after reaction.

original bed material was very smooth except for some minor impurities. However, the surface of the postreaction bed material was covered with particles whose diameters were approximately 1−10 μm, which was similar to the diameters of the Ca(OH)2 particles in the lime slurry. The main chemical element compositions on the surface of the original bed material and postreaction bed material were measured by EDS (Table 2). The main chemical elements on the surface of the original bed material were Si and O, which agreed with the Table 2. Chemical Element Composition on the Surface of the Bed Material content (%) original postreaction

C

O

Si

Mg

S

Ca

2.34 2.86

57.11 19.59

40.55 2.38

1.48

27.08

46.62 D


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Energy & Fuels Table 3. Chemical Composition of the Postreaction Bed Material chem composn

SiO2

CaO

S

MgO

Al2O3

P2O5

Fe2O3

Na2O

content (%)

82.74

9.84

4.59

1.56

0.70

0.17

0.13

0.12

1.70%. As the Ca/S molar ratio increased to 2.37, the mass fraction of water in the flue gas increased to approximately 3.7%. According to previous research on semidry desulfurization,33,34 at high mass fraction of water, desulfurization efficiency varies little with operation conditions. Water content in flue gas became the dominant parameter for the desulfurization reaction. So when the Ca/S molar ratio was high, the effect of the slurry spray method on desulfurization efficiency was less than that when the Ca/S molar ratio was low. For the countercurrent slurry spray, the desulfurization system ran stably and scaling of the reactor wall was not observed. The possible reason for the good operating stability was the high solid volume fraction around the slurry sprayer, which prevented slurry droplets depositing on the reactor wall. Furthermore, the average temperature in the reactor was approximately 110−150 °C (significantly higher than that of the usual semidry desulfurization process, 80−120 °C11,35), which accelerated evaporation of the spray droplets. 3.3. Desulfurization Performance of Supported Sorbent. Figure 7 shows typical SEM micrographs for the original silica sand and the supported sorbent prepared by the

Figure 5. Effect of slurry sprayer height above distributor on desulfurization efficiency.

current may cause operation instability.32 However, countercurrent has the benefit of effective contact between the lime slurry droplets and the bed material, which results in high adhesion efficiency of ultrafine Ca(OH)2 particles on the bed material surface.23 The effect of the slurry spray method on desulfurization efficiency and operation stability was studied, with a slurry sprayer located 0.1 m above the distributor. Figure 6 showed the desulfurization efficiency of these two spray

Figure 6. Effect of slurry spray method on desulfurization efficiency.

methods at different Ca/S molar ratios. With the Ca/S molar ratio at 1.09−2.37, the desulfurization efficiency was 19.3− 87.6% for the co-current slurry spray. The desulfurization efficiency for the countercurrent slurry spray was approximately 20% higher than that of the co-current slurry spray at a relatively low Ca/S molar ratio. When using countercurrent slurry spray, effective contact between lime slurry droplets and bed material particles led to higher adhesion efficiency, which resulted in higher desulfurization efficiency. For a higher Ca/S molar ratio, the desulfurization efficiency for the countercurrent slurry spray was higher than that of the co-current slurry spray for only 5−10% because the water content in the flue gas increased with Ca/S molar ratio. When Ca/S molar ratio was 1.09, the mass fraction of water in flue gas was approximately

Figure 7. SEM micrographs: (a) original bed material; (b) supported sorbent. E


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Energy & Fuels

sorbent was longer than the lime slurry spray semidry desulfurization process. However, the desulfurization efficiency of the supported sorbent was lower than that of the lime slurry spray semidry desulfurization process because of its lower contact efficiency between water droplets and the sorbent. The effective contact of water droplets and sorbent was particularly important for semidry desulfurization.12 For the lime slurry spray semidry desulfurization process, water and Ca(OH)2 were fed together by the slurry sprayer. The contact efficiency for the lime slurry spray method was much higher than that of the supported sorbent desulfurization process, where the supported sorbent and spray water were separately fed at different locations. For a high Ca/S molar ratio, the desulfurization efficiency of the lime slurry spray semidry desulfurization was 30−40% higher than that of the supported sorbent semidry desulfurization process. This was because the contact efficiency of the water droplets and Ca(OH)2 became more significant when water content in the flue gas was high at a high Ca/S molar ratio.

hydration and drying process. The surface of the original silica sand is very smooth except for some minor impurities. However, the surface of the supported sorbent is very rough, being full of tiny particles and particle agglomerates. These particles and particle agglomerates are mainly formed by Ca(OH)2 crystallization that occurs during the preparation process. Some of the particles in the supported sorbent have diameters that are noticeably smaller than the original silica sand, which agrees with the particle size distribution analysis. It indicates that some Ca(OH)2 particles do not adhere to the surface of the silica sand during the original hydration and drying process. Figure 8 shows the desulfurization performance of the supported sorbent and the lime slurry spray semidry

4. CONCLUSION A lime slurry spray semidry desulfurization process with in situ supported sorbent preparing was studied in a pilot-scale CFB reactor. Effects of different operation parameters on the desulfurization performance were investigated. And desulfurization efficiency of this proposed semidry desulfurization process was compared with supported sorbent prepared by the original hydration method. From the results of the present study we concluded the following: (1) Desulfurization efficiency can reach 98.84% at Ca/S = 2.5 with countercurrent spray method when the bed inventory is 28 kg, seven times higher than that without bed material. The main reason for the high desulfurization efficiency is that some ultrafine Ca(OH)2 particles in the lime slurry adhere to the bed material surface which forms the supported sorbent. The residence time of these ultrafine Ca(OH)2 particles are pretty long which results in high desulfurization efficiency. High bed inventory leads to high desulfurization efficiency. (2) The height of the sprayer above the distributor affects desulfurization efficiency by effecting adhesion efficiency of ultrafine Ca(OH)2 particles. The calcium conversion rate for h = 0.1 m is approximately 10−15% higher than that of h = 0.9 m. (3) Desulfurization efficiency for the countercurrent slurry spray is higher than that of the co-current slurry spray for approximately 20% at low Ca/S molar ratio and approximately 5−10% at high Ca/S molar ratio. For this proposed semidry desulfurization process, the desulfurization system ran stably and scaling of the reactor wall was not observed when using countercurrent slurry spray. So countercurrent slurry spray is preferred for industry application. (4) The desulfurization efficiency of this proposed lime slurry spray semidry desulfurization process is higher than the supported sorbent prepared by the original hydration method for approximately 5−10% at low Ca/S molar ratio and approximately 30−40% at high Ca/S molar ratio, because of its effective contact of water droplet and sorbent. For industry application, this proposed process is preferred more than the original hydration method for its high desulfurization efficiency and simple processing.

Figure 8. Desulfurization performance of supported sorbent and lime slurry spray semidry desulfurization process.

desulfurization process with countercurrent spray. The water sprayer is approximately 0.3 m above the sorbent feeder. The mass ratio of the water to Ca(OH)2 in the supported sorbents is 3.87−4.70, which is similar to the mass ratio of water to Ca(OH)2 in the lime slurry that is used by the lime slurry spray semidry desulfurization process. At a specified Ca/S molar ratio, the water content in the flue gas of the two semidry desulfurization processes is almost the same. When the Ca/S molar ratio was 0.92−2.22, the desulfurization efficiency was 29.9−58.8% for the supported sorbent. The desulfurization efficiency of the lime slurry spray semidry desulfurization was 5−10% higher than that of the supported sorbent for a low Ca/ S molar ratio. SEM micrograph and particle size distribution analysis of the supported sorbent indicated that there was only a minor quantity of Ca(OH)2 particles that did not adhere to the silica sand surface, with the majority adhering during the hydration and drying process. As discussed above, many Ca(OH)2 particles in the lime slurry still did not adhere to the bed material surface and these Ca(OH)2 particles then escaped from the CFB reactor before reacting with SO2 for the lime slurry spray semidry desulfurization process. The contact efficiency of Ca(OH)2 particles with silica sand was higher for the original hydration and drying method. The adhesion efficiency of Ca(OH)2 particles for the supported sorbent prepared by the hydration and drying process was higher than that of the lime slurry spray semidry desulfurization process. Therefore, more Ca(OH)2 particles could be sent back to the main bed by the cyclone separator for the supported sorbent than the lime slurry spray semidry desulfurization process. The overall residence time of Ca(OH)2 particles for the supported F


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AUTHOR INFORMATION

Corresponding Author

*Telephone: +86-10-62785669. E-mail: [email protected]. cn. ORCID

Changfu You: 0000-0003-4174-2177 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS

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REFERENCES

This research was supported by the National Natural Science Foundation of China (Grant 51476089), the National Key Research and Development Program (Grant 2016YFC0204103), and the Key Science and Technology Project for Coal of Shanxi Province (Grant MD2014-03).

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Energy & Fuels (35) Liu, J.; Gao, J.; Jiang, X.; Gao, J.; Du, Q.; Wu, S. Simultaneous removal of SO2 and small particles in a multistage spouted fluidized tower. Energy Fuels 2009, 23 (12), 5934−5941.

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Semi-dry Desulfurization Process with In Situ Supported Sorbent

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