Dry Desulfurization Research Articles

Analysis of pressure fluctuation signals in the underfeed circulating spouted bed

The underfeed circulating spouted bed (UCSB) was designed as a new dry desulfurization reactor. In this article, pressure fluctuations along the axial direction were measured and time, frequency and Shannon entropy analysis of pressure signals were studied under different operation parameters. The results indicate: the pressure fluctuations express different characteristics at various axial locations. And the operation parameters have significant influence on the flow characteristic in the riser. Advancing the spouting velocity or the circulating ratio, the solid concentration in the riser increases and the amplitude of the pressure fluctuations rises. With higher injecting velocity or nozzle position, the gas–solid turbulence in the bottom bed gets more intense. It shows that the existence of injecting flow near the underfeed nozzle has a distinct effect on strengthening the particle mixing. The power spectrum density acquired from the signals can coincidently reflect the dynamic behavior of the gas–solid flow in the riser. Analysis of Shannon entropy also corresponds to the above summarization of flow characteristic very well.

Improvement of Desulfurization Performances of Waste Cement Particles by Acid Treatment

We studied the effect of acid treatments on the desulfurization rate of waste cement, a byproduct in the recycling of aggregates from waste concrete. Calcium components in the waste cement were partially extracted by treatment with carbonic acid (aqueous solution of high-pressure CO2), hydrochloric acid, or acetic acid. The desulfurization rate was examined using a thermogravimetric method. The desulfurization rates in the initial stage of the reaction (<5 min) were almost unaffected by the treatments with acetic acid and hydrochloric acid, provided the degree of calcium extraction was lower than about 30%. However, the desulfurization rates at a later stage were lower than that of the original waste cement. The desulfurization rates of the waste cement treated with carbonic acid were higher than those of the original sample for all reaction times studied when the degree of calcium extraction was in the range of 4.13−8.54%. The desulfurization rate normalized by the amount of calcium remaining in the waste cement was higher for all samples with acid treatment than for the original sample when the degree of calcium extraction was lower than 60%. The desulfurization rates of the acid-treated waste cements were significantly higher than that of limestone, a conventional sorbent used in dry desulfurization.

Desulfurization Characteristics of Waste Cement Particles as a Sorbent in Dry Desulfurization

Dry desulfurization characteristics of waste cement particles were examined with laboratory-scale experimental apparatus based on the weight change of the sample exposed to a gas flow containing SO2. The waste cement particles, a byproduct of recycling aggregates from waste concrete, are fine particles with diameters ranging from 10 to 200 μm and an average diameter of 105 μm. The effects of the operation parameters, i.e., the reaction temperature (650−950 °C), SO2 concentration (61−1543 ppm), oxygen concentration (0−10%), NO2 concentration (0−500 ppm), absolute humidity (0−15000 ppm), and particle size (10−200 μm), on the desulfurization performance were investigated. The desulfurization rates were found to depend on the 1.26th order of the SO2 concentration and to slightly depend on the absolute humidity and the particle size, but they were almost independent of the concentrations of oxygen and NO2 in the gas flow. Arrhenius type temperature dependence was observed up to 850 °C with activation energy of 12 kJ/mol. The observed dry desulfurization rates of the waste cement particle were almost equivalent to those of the conventional sorbents such as limestone and calcium hydroxide. Therefore, it is confirmed that the waste cement particles could be applicable in dry desulfurization as an inexpensive sorbent derived from wastes.

Effect of Operating Parameters and Reactor Structure on Moderate Temperature Dry Desulfurization

A moderate temperature dry desulfurization process at 600-800 degrees C was studied in a pilot-scale circulating fluidized bed flue gas desulfurization (CFB-FGD) experimental facility. The desulfurization efficiency was investigated for various operating parameters, such as bed temperature, CO2 concentration, and solids concentration. In addition, structural improvements in key parts of the CFB-FGD system, i.e., the cyclone separator and the distributor, were made to improve the desulfurization efficiency and flow resistance. The experimental results show that the desulfurization efficiency increased rapidly with increasing temperature above 600 degrees C due to enhanced gas diffusion and the shift of the equilibrium for the carbonate reaction. The sorbent sulfated gradually after quick carbonation of the sorbent with a long particle residence time necessary to realize a high desulfurization ratio. A reduced solids concentration in the bed reduced the particle residence time and the desulfurization efficiency. A single-stage cyclone separator produced no improvement in the desulfurization efficiency compared with a two-stage cyclone separator. Compared with a wind cap distributor, a large hole distributor reduced the flow resistance which reduced the desulfurization efficiency due to the reduced bed pressure drop and worsened bed fluidization. The desulfurization efficiency can be improved by increasing the collection efficiency of fine particles to prolong their residence time and by improving the solids concentration distribution to increase the gas-solid contact surface area.

Dry Desulfurization in a Circulating Fluidized Bed (CFB) with Chain Reactions at Moderate Temperatures

A series of experiments in a circulating fluidized bed (CFB) pilot plant has explored a new dry desulfurization process, using the NO x in the flue gas and a new sorbent that has been prepared from fly ash and lime. Various desulfurization operating parameters were tested for the thermodynamic, chemical, and dynamic states for temperatures of 523-673 K. The NO x increased the calcium conversion ratio in the desulfurization process. In addition, with the NO x , the desulfurization byproduct was determined to be mostly CaSO 4 , instead of CaSO 3 , as a result of the chain reaction caused by the NO x . Therefore, the NO x in the flue gas can improve the efficiency of the dry desulfurization process.

Novel Dry-Desulfurization Process Using Ca(OH)2/Fly Ash Sorbent in a Circulating Fluidized Bed

A dry-desulfurization process using Ca(OH)2/fly ash sorbent and a circulating fluidized bed (CFB) was developed. Its aim was to achieve high SO2 removal efficiency without humidification and production of CaSO4 as the main byproduct. The CaSO4 produced could be used to treat alkalized soil. An 83% SO2 removal rate was demonstrated, and a byproduct with a high CaSO4 content was produced through baghouse ash. These results indicated that this process could remove SO2 in flue gas with a high efficiency under dry conditions and simultaneously produce soil amendment. It was shown that NO and NO2 enhanced the SO2 removal rate markedly and that NO2 increased the amount of CaSO4 in the final product more than NO. These results confirmed that the significant effects of NO and NO2 on the SO2 removal rate were due to chain reactions that occurred under favorable conditions. The amount of baghouse ash produced increased as the reaction progressed, indicating that discharge of unreacted Ca(OH)2 from the reactor was suppressed. Hence, unreacted Ca(OH)2 had a long residence time in the CFB, resulting in a high SO2 removal rate. It was also found that 350 degrees C is the optimum reaction temperature for dry desulfurization in the range tested (320-380 degrees C).

03/02117 Investigation of partial oxidation of hydrogen sulfide for dry desulfurization of fuel gases: Kliemczak, U. Freiberger Forschungshefte A, 2002, A868, 1–226. (in German)

03/02117 Investigation of partial oxidation of hydrogen sulfide for dry desulfurization of fuel gases: Kliemczak, U. Freiberger Forschungshefte A, 2002, A868, 1–226. (in German)

Development of White-Biocoalbriquettes with High Desulfurization Function

To control the pollutant emission from coal combustion from both domestic stoves and middle- and small-scale boilers in some developing countries, an artificial solid fuel called biocoalbriquette was researched and developed experimentally. However, it is necessary to further increase the desulfurization efficiency of the biocoalbriquette in order to effectively popularize it in these countries. For this reason, white-biocoalbriquette was proposed and researched in this study for a more effectively and economically artificial solid fuel. This white-biocoalbriquette is a composite solid fuel of both coal and biomass. A little limestone is mixed in its inside, and its surface is coated by a thin layer of desulfurizer. The white-biocoalbriquette looks white and will change people's traditional concept of coal from black and dirty to new and clean. The experimental results show that the white-biocoalbriquette has successfully improved the desulfurization characteristics for this kind of artificial solid fuel from coal due to effectively controlling SO2 emission in both volatile combustion and char combustion. The temperature fluctuation in a combustion chamber hardly has an obvious influence on the desulfurization efficiency. Finally, the desulfurization efficiency of the white-biocoalbriquette has been achieved nearly 90%. At present, it is the highest desulfurization efficiency in a dry desulfurization process.

H2S Removal by Fine Limestone Particles in a Powder−Particle Fluidized Bed

An efficient dry desulfurization process for hot coal gas was proposed. The process uses a powder-particle fluidized bed as the reactor, in which coarse particles of several hundred micrometers are fluidized via hot gas consisting of H2S, H2, and N2 while fine limestone particles are fed continuously into the bed. Fine limestone particles of less than 30 μm were used as H2S sorbent. The effects of operating parameters on the H2S removal efficiency were investigated. Desulfurization via 5-μm limestone was very effective, demonstrating over 90% H2S removal at 1073 K for the case of Ca/S = 2, even under the conditions of a very short residence time (0.3 s) of gas in the bed. Investigation of the sorbent pore structure before and after calcination and desulfurization revealed the correspondence of higher specific surface area of CaO to higher H2S removal efficiency.

Calcined calcium magnesium acetate as a superior SO2 sorbent: I. Thermal decomposition

AbstractThe reactivity of the calcination product of calcium magnesium acetate (CMA) as a possible dry desulfurization agent was evaluated. The first step in the dry desulfurization reaction—the thermal decomposition of CMA—was investigated by determining the decomposition reaction in three steps: 1. the evaporation of water starting at 65°C, 2. the conversion of CMA into CaCO3 and MgO starting at 275°C, and 3. the decomposition of CaCO3 to CaO starting at 580°C. The pseudo‐first‐order kinetic equation was observed for the CMA decomposition to CaCO3 + MgO, with an activation energy of 165.5 kJ/mol. The decomposition of CaCO3 to CaO also obeyed the pseudo‐first‐order kinetics, with an activation energy of 200 kJ/mol. As discussed in Part II of this series, the calcination product from CMA is quite reactive due mainly to the large porosity and internal surface area generated on the removal of the acetate group during the decomposition reaction. Furthermore, as will be shown in Parts II and III, the sulfation capacity of the calcined CMA is much greater than that of conventional sorbents because its sulfation rate does not level off until complete conversion and its MgO content is also sulfated at temperatures lower than about 900°C.

A Surface coverage Model for the Reaction of Ca(OH)2 with SO2 at Low Temperatures

Hydrated lime (Ca(OH)2) is widely used as a sorbent in the dry and spray-drying flue gas desulfurization processes. The reaction of Ca(OH)2 with SO2 at low temperatures in these processes is well described by the equations obtained from a surface coverage model. The model assumes that the rate is controlled by the chemical reaction occurring on the water-adsorbed sorbent surface and considers the surface coverage by the product. The results of this study are useful for the design and operation of dry and spray-drying processes using hydrated lime.

Preparation, Characterization, and Calcium Utilization of Fly Ash/Ca(OH)2 Sorbents for Dry Desulfurization at Low Temperature

Sorbents for SO2 removal were prepared by hydration at 90 °C of calcium hydroxide and coal fly ash at different fly ash/Ca(OH)2 initial ratios, from 1/3 to 15/3, and slurring times, from 3 to 37 h. Properties characterized in the sorbents included the particle size, the Brunauer−Emmett−Teller surface area, and the porosity distribution. The Ca(OH)2 conversion as a measure of the pozzolanic reaction extent was also determined; all of these sorbent properties were related to the preparation variables. The obtained sorbents were tested in a flue gas desulfurization reaction at 57 °C and 52% relative humidity. The calcium utilization in this reaction was quantified as moles of SO2 captured per moles of calcium × 100. The Ca(OH)2 conversion in the hydration reaction and the raw material ratios have been revealed as the most efficient parameters to predict the behavior of the sorbent in the desulfurization process. The hydration reaction between fly ash and Ca(OH)2 should be performed just until the completion of the pozzolanic reaction and with a fly ash/Ca(OH)2 initial weight ratio of 5/3 or 9/3 to have an optimum sorbent in the reaction with SO2.

Chain Reaction Mechanism by NOx in SO2 Removal Process

The effects of NOx, CO2, and reaction temperature on the SO2 removal process have been investigated in a fluidized bed reactor by using CaO/fly ash sorbent in order to demonstrate any available method to promote the calcium utilization rate and form valuable gypsum as a byproduct for the dry desulfurization process. It was found that NOx increased the selectivity of CaSO4 as the final product in the sorbent during the desulfurization process. The effect of NOx on SO2 removal rate was also investigated and results showed that the presence of NOx enhanced the SO2 removal rate, even when mole ratio of NO/SO2 was less than 1.0. It was deduced that the reaction mechanism involved NOx-related chain reactions. On the basis of FTIR analysis of reactions product, the chain reaction mechanism could be outlined that Ca(NO3)2 was formed from the reaction of Ca(OH)2 with NO2, and then Ca(NO3)2 reacts with SO2 to form CaSO4 + NO. On the other hand, it was found that the CO2 negative effect on SO2 removal was reduced wi...

Effect of CaSO 4 on the structure and use of Ca(OH) 2/fly ash sorbents for SO 2 removal

Sorbents for SO 2 removal from flue gas were prepared by hydration of fly ash, calcium hydroxide and calcium sulfate to simulate the reuse of desulfurant sorbents after reactivation, at different relative amounts and slurrying times. They were characterized by determining the specific surface area and pore volume distribution, and tested in the dry desulfurization reaction at low temperature. The purpose was to investigate the influence of CaSO 4 in the system fly ash/calcium hydroxide, following the physical properties of the sorbents as well as the sorbent utilization in the desulfurization reaction. The sorbents prepared with CaSO 4 showed structural properties and chemical composition that were different from those of sorbents without CaSO 4 (with in general less specific surface area and mesopore volume). Sorbent utilization was expressed in two ways: as utilization of calcium hydroxide (mol of captured SO 2/g of Ca(OH) 2) and as total calcium utilization (total SO 2 mol in the sorbent/total calcium mol in the sorbent). In the desulfurization test, all the sorbents prepared with and without CaSO 4, at different fly ash/calcium hydroxide/calcium sulfate ratios and slurrying times, showed a great increase in the calcium utilization compared with commercial calcium hydroxide. The utilization of calcium hydroxide showed lower values for sorbents with CaSO 4 than for sorbents without CaSO 4. For all the sorbents studied, with and without CaSO 4, a near to constant ratio of 70% of total calcium utilization was found. These results show that despite the different chemical composition and structural properties, only the total calcium amount determines the sorbent capacity for desulfurization.

Applying Eulerian and Lagrangian Approaches to the Modeling of Dry Desulfurization Process in Pulverized Coal Furnaces

The dry additive desulfurization process (DAP) is an appropriate approach for SO X -reduction in power plants with small and medium capacity and for the retrofit of existing boilers with spatial limitations. In engineering practice, it can be optimized by means of numerical modeling. In the present work, a comprehensive model for simulating the DAP in pulverized coal furnaces is established. A pore model (PM)3069 is suggested to describe the gas-solid reaction between the sorbent and SO X . The overall DAP model is implemented into a coal combustion simulation CFD program AIOLOS, because of the feature of two-phase-flow of DAP, in both Eulerian and Lagrangian (particle tracking) schemes. DAP-desulfurization in engineering processes can be simulated. Numerical studies were performed through various calculations with both Eulerian and Lagrangian approaches for a small-scale furnace. The behaviors and results of the two approaches were compared. The present DAP model offers reasonable results. In addition, it was found: (a) For sorbent particles finer than 60-70 μm, quite similar desulfurization results can be obtained from the two modeling schemes. Above this size range the slip between phases shows significant influence. (b) The CPU-time of the Lagrangian approach increases rapidly with decreasing particle size below about 30 μm. In the present study with 400 tracing particles, the Lagrangian approach requires less computing time than Eulerian above particle size of 60-70 μm. (c) The Lagrangian approach is more suitable for handling two-phase flow with detailed particle size distributions. The Eulerian approach has advantages for treating flows with finer particle suspensions. (d) The Eulerian scheme has less convergence problems, whereas the Lagrangian approach is more sensitive to the computation procedure and requires small relaxation factors.

The reduction of gas phase air toxics from combustion and incineration sources using the MET–Mitsui–BF activated coke process

The dry desulfurization, denitrification and air toxics removal process using activated coke (AC) was originally researched and developed during the 1960s by Bergbau Forschung (BF) [Knoblaugh, E. Richter, H. Juntgen, Application of active coke in processes of SO x and NO x removal from flue gases, Fuel 60, September 1981, p. 832.], now called Deutsche Montan Technologies. Mitsui Mining (MMC) signed a licensing agreement with BF in 1982 to investigate, test and adapt the system to facilities in Japan. Japanese regulations are stricter than in the United States toward SO x /NO x pollutants, as well as flyash emissions from the utility industry, oil refineries and other industries. This process is installed on four coal-fired boilers and Fluidized Catalytic Cracker (FCC) units. These plants were constructed by MMC in Japan and Uhde in Germany. Two additional plants on a utility boiler and cement kiln are scheduled to start operation in 1999 and 2000. MMC provided design, equipment supply and installation. Marsulex Environmental Technologies (MET) formerly General Electric Environmental Services (GEESI) signed a license agreement in 1992 with MMC and Mitsui of Tokyo. Under this agreement, MET will market, design, fabricate and install the Mitsui–BF process for flue gas cleaning applications in North America. MMC also developed a technology to produce AC used in the dry DeSO x /DeNO x /Air Toxics removal process based on their own metallurgical coke manufacturing technology. This paper provides information on the details of MMC's AC used in the dry DeSO x /DeNO x /Air Toxics removal process and of the DeSO x /DeNO x /Air Toxics removal process itself.

99/03072 Apparatus for dry desulfurization of fuel gases at high temperatures

99/03072 Apparatus for dry desulfurization of fuel gases at high temperatures

99/02947 Integrated coal-gasification combined with power generation system and method for adopting of regenerated air from dry desulfurization tower

99/02947 Integrated coal-gasification combined with power generation system and method for adopting of regenerated air from dry desulfurization tower

Dry Desulfurization of Simulated Flue Gas in a Fluidized-Bed Reactor for a Broad Range of SO2 Concentration and Temperature: A Comparison of Models

In this work, dry desulfurization of simulated flue gas was investigated in a batchwise operated laboratory-scale stainless steel fluidized-bed reactor (46 × 500 mm2) by using calcium-containing local Turkish limestone (Karaaǧaçlı/MUS) which was calcined at 900 °C with 5% H2O vapor. The sulfation reaction was carried out in a broad range of temperature (200 ≤ T(°C) ≤ 900) and SO2 feedstock concentration (1000 ≤ C(ppm SO2) ≤ 6000). The experimental sulfation conversion-time data were tested according to unreacted shrinking core model (SCM), changing the grain size model (GM) and random pore model (RPM). It was found that the random pore model with control of product layer (CaSO3/CaSO4) diffusion described the experimental data best.

High Calcium Utilization and Gypsum Formation for Dry Desulfurization Process

The high-active sorbent for SO2 removal was developed by mixing CaO particles with fly ash in water at ambient temperature. The calcium utilization rate in the sorbent was achieved to 60% after the desulfurization reaction at 450 °C for 90 min, while the utilization rate for original pure CaO particles was only 21% under the identical conditions. The surface of the sorbent was examined by SEM, EDX, and BET analysis to study the activation mechanism. Results indicated that CaO particles were separated to several small particles of Ca(OH)2 in water due to a significant heat release, while a small amount of Ca(OH)2 dissolved in water. Under the condition of coexistence with fly ash particles, the tiny Ca(OH)2 particles and its solute covered the surface of fly ash particles with the drying process. Therefore, SO2 could react efficiently with the Ca(OH)2 on the surface of fly ash particles. XRD analysis showed that the composition of sorbent was not apparently changed in the sorbent preparation process. Moreover, the mixture time of CaO and fly ash in water did not play a significant role on calcium utilization rate. These results revealed that the hydration reactions between CaO and the materials such as SiO2 or Al2O3 in fly ash were limited in sorbent preparation process at ambient temperature. The IR analysis of reaction products indicated that gypsum could be produced efficiently at high reaction temperature by using the sorbent.