Sorbent Injection Technology Research Articles

Experimental Study on Desulfurization Characteristics of Dry Sorbent Injection at Low SO2 Concentrations

AbstractTo effectively reduce SO2 emissions, flue gas desulfurization methods are widely used in coal‐fired power plants. In desulfurization, the dry sorbent injection (DSI) technology has the advantages of high desulfurization efficiency, simple operation, convenient adjustment, and low initial investment. Here, a pilot‐scale experimental system was designed and built to investigate the desulfurization characteristics of the DSI technology. The influence of the residence time of the desulfurizer, the reaction temperature, the stoichiometric ratio of the desulfurization reaction, the particle size of the desulfurizer, the inlet SO2 concentration, the dust concentration, and the water vapor content in the flue gas on the desulfurization efficiency at low SO2 concentrations was studied by injecting NaHCO3 into the pipeline. The desulfurization efficiency can be significantly improved by reducing the desulfurizer particle size or increasing the water vapor content in the flue gas at low SO2 concentration. An empirical formula describing the dependence of the desulfurization efficiency on experimental parameters is given.

Co-doped ZnS with large adsorption capacity for recovering Hg0 from non-ferrous metal smelting gas as a co-benefit of electrostatic demisters.

The installation of electrostatic demisters (ESDs) makes possible the use of sorbent injection technology for recovering Hg0 from non-ferrous smelting gas. ZnS, as a typical smelting raw material, could be a promising candidate due to the sulfur boding site for mercury. However, the low reaction rate and poor adsorption capacity limited its application. In this study, Co was incorporated into ZnS to enhance adsorption activity for recovering Hg0. Co0.2Zn0.8S exhibited the best Hg0 capture performance among the modified sorbents. The Hg0 adsorption capacity was up to 46.01mg/g at 50°C (with 50% breakthrough threshold), and the adsorption rate was as high as 0.017mg/(gmin). Meanwhile, SO2 and H2O had no poison effects on Hg0 adsorption. The chemical adsorption mechanism was proposed, which was Co3+, and sulfur active sites could immobilize Hg0 in the form of stable HgS, following a Mars-Maessen reaction pathway. The spent sorbent will release ultrahigh concentration mercury-containing vapor through the heating treatment, which facilitated centralized recovery of Hg0. Meanwhile, inactivated sorbent can be used as smelting raw material to recover sulfur resources. Therefore, the control of Hg0 emission from non-ferrous smelting gas by Co-adopted ZnS was cost-effective and did not form secondary pollution. Graphical abstract.

Enhanced Hydrated Lime—A Simple Solution for Acid Gas Compliance

The U.S. landscape of environmental regulations is complex and continues to evolve requiring more stringent acid gas emission limits than ever. Current regulations include acid gas emission requirements via the Portland Cement National Emission Standard for Hazardous Air Pollutants, consent decrees, and revised operating permits, where operational modifications are made requiring additional acid gas removal. As a result of the need to comply with these increasingly stringent acid gas emission limits, there is a growing desire for a relatively simple solution. Dry sorbent injection (DSI) technology offers a low capital cost solution with a relatively small equipment footprint, low power consumption, and ease of retrofit to a majority of existing facilities. As DSI technology has matured, the systems have become more reliable and advancements in calcium based sorbents have provided new compliance solutions that were not available in past years. The optimization of the physical properties of enhanced hydrated lime products has demonstrated upward of 90% sulfur dioxide and 95+% hydrochloric acid reduction with the DSI technology over a range of applications, and has been consistently successful achieving cement plant's acid gas removal needs to meet their regulatory requirements.

UNEP Demonstrations of Mercury Emission Reduction at Two Coal-fired Power Plants in Russia

The United Nations Environment Programme (UNEP) partnership area “Mercury releases from coal combustion” (The UNEP Coal Partnership) has initiated demonstrations of mercury air emission reduction at two coal-fired power plants in Russia. The first project has modified the wet particulate matter (PM) scrubber installed in Toliatti thermal plant to allow for addition of chemical reagents (oxidants) into the closedloop liquid spray system. The addition of oxidant resulted in significant improvement of mercury capture from 20% total mercury removal (without the additive) up to 60% removal (with the additive). It demonstrates the effectiveness of sorbent injection technologies in conjunction with an electrostatic precipitator (ESP). ESPs are installed at 60%, while wet PM scrubbers are installed at 30% of total coal-fired capacity in Russia. Thus, the two UNEP Coal Partnership projects address the majority of PM emission control configurations occurring in Russia.

10.2478/s11814-009-0297-1

The aim of this study is to improve mixing rate of dry sorbent injection technology (DSI). A CFD (Computational Fluid Dynamics) code is used to predict the sorbent dispersion rate, pressure drop and turbulent kinetic energy of mixing particles and gas flow for three different vortex generators, which have been designed for the inside of the duct. After analyzing simulated results, it was shown that a similar trend of change in the dispersion rate in three different vortex generators had taken place and that the dispersion rate curve could reach over 80% by applying the lobed-plate and guide-vane(B) vortex generators. The lowest pressure drop was obtained when a lobed-plate was installed, whereas the highest pressure drop occurred when a guide-vane(A) was installed. The turbulent kinetic energy is nearly always stable when a lobed-plate is applied, but increases very quickly after passing through a guide-vane and then slowly decreases when a guide-vane(B) is applied. The situation for in the case of guide-vane(A) is somewhat more complicated.

A study on vortex generators to improve the mixing rate in the dry sorbent injection process of the flue gas desulfurization system

The aim of this study is to improve mixing rate of dry sorbent injection technology (DSI). A CFD (Computational Fluid Dynamics) code is used to predict the sorbent dispersion rate, pressure drop and turbulent kinetic energy of mixing particles and gas flow for three different vortex generators, which have been designed for the inside of the duct. After analyzing simulated results, it was shown that a similar trend of change in the dispersion rate in three different vortex generators had taken place and that the dispersion rate curve could reach over 80% by applying the lobed-plate and guide-vane(B) vortex generators. The lowest pressure drop was obtained when a lobed-plate was installed, whereas the highest pressure drop occurred when a guide-vane(A) was installed. The turbulent kinetic energy is nearly always stable when a lobed-plate is applied, but increases very quickly after passing through a guide-vane and then slowly decreases when a guide-vane(B) is applied. The situation for in the case of guide-vane(A) is somewhat more complicated.

Evaluation of low ash impact sorbent injection technologies for mercury control at a Texas lignite/PRB fired power plant

A sorbent injection test program was carried out at NRG Texas Power LLC's (NRG) Limestone Electric Generating Station (LMS). LMS fires a 30/70 blend of Powder River Basin (PRB) and Texas Lignite, and is equipped with a cold-side electrostatic precipitator (ESP) and wet scrubber. The plant markets its fly ash for beneficial use, so development of a low ash impact mercury control technology is important to the economics of implementing a mercury control system. In addition to standard activated carbon injection, two different low ash impact mercury control technologies were evaluated in parametric tests: low ash impact sorbents and Toxecon™ II. The parametric ACI test program conducted at LMS demonstrated that high (>90%) levels of mercury removal could be achieved with carbon sorbents. The Toxecon™ II design used at LMS did not provide for as high a mercury removal as injection upstream of the ESP, likely due to poor coverage of the cross-sectional area of the ESP. Limited concrete testing was performed with simulated ash/carbon mixtures. As expected, the amount of air-entraining additive required increased with increasing carbon content in the ash. However, it appeared that small amounts of non-passivated carbon may be acceptable in fly ash for concrete use.

Modeling of the in-duct sorbent injection process for flue gas desulfurization

Dry scrubbing processes, especially dry sorbent injection technology, offer a more economical technology for retrofitting than wet or semi-wet scrubbing processes. A simple realistic model for the in-duct desulfurization process has been developed. The model has been conceived as an approach useful for both analyzing results and aiding in design of an in-duct desulfurization process. The model of the process involved, which is the basis for the discussion in this paper, has been evaluated by comparing the model results and the experimental data, obtained in a pilot plant study. The predicted values agree reasonably well with the available experimental data, and the relationships in the model presented have been verified. The sensitivity analysis of variables is relevant for the design and operation of the in-duct process, allowing a parametric study that reveals the effect of the different operation and design factors. Although this model is specific to our in-duct pilot plant, it may be used with confidence in commercial DSI (dry sorbent injection) units as it was designed and implemented according to widely accepted engineering rules in this field. The model has been built in an open structure to allow for rearrangements of and extensions to the process.

A technique to control mercury from flue gas: The Thief Process

The Thief Process is a mercury removal process that may be applicable to a broad range of pulverized coal-fired combustion systems. This is one of several sorbent injection technologies under development by the U.S. Department of Energy for capturing mercury from coal-fired electric utility boilers. A unique feature of the Thief Process involves the production of a thermally activated sorbent in situ at the power plant. The sorbent is obtained by inserting a lance, or thief, into the combustor, in or near the flame, and extracting a mixture of partially combusted coal and gas. The partially combusted coal or sorbent has adsorptive properties suitable for the removal of vapor-phase mercury at flue gas temperatures that are typical downstream of a power plant preheater. One proposed scenario, similar to activated carbon injection (ACI), involves injecting the extracted sorbent into the downstream ductwork between the air preheater and the particulate collection device of the power plant. Initial laboratory-scale and pilot-scale testing, using an eastern bituminous coal, focused on the concept validation. Subsequent pilot-scale testing, using a Powder River Basin (PRB) coal, focused on the process development and optimization. The results of the experimental studies, as well as an independent experimental assessment, are detailed. In addition, the results of a preliminary economic analysis that documents the costs and the potential economic advantages of the Thief Process for mercury control are discussed.

Emission control of sodium compounds and their formation mechanisms during coal combustion

In order to control emissions of sodium compounds during coal combustion, the sorbent injection technology is tested during coal combustion. Kaolin is selected as the sorbent to absorb vapors of sodium compounds evolved from the coals. In the combustion experiments, the kaolin is physically mixed with coal. Two types of coal, which have the similar coal properties, are burned. Combustion tests are conducted, using an electrically heated drop tube furnace, to study effect of kaolin addition on the capture characteristics of sodium compounds. In order to elucidate fundamentals on transformation behaviors of sodium compounds during hydrogen–air combustion, chemical kinetic simulation by elementary reactions relating to sodium compounds is also performed, varying the reaction atmosphere. As a result, the kaolin can effectively capture the vapor of sodium compounds even during coal combustion. The capture efficiency depends on the coal type. The sodium compounds for the coals, which produce many fine particles with size of less than 1 μm, tend to be effectively captured by the kaolin. According to the kinetic simulation of sodium species, difference of the reaction atmosphere affects occurrence species of sodium vapor. In the combustion region, the sodium compounds become metallic sodium vapor in any reaction atmospheres due to occurrence of the reducing radical species. HCl gas rather than SO 2 gas plays an important role to transform gaseous sodium compounds.

311 カオリンの微量添加による石炭燃焼場における微粒子生成およびアルカリ金属化合物の制御(大気汚染物質除去,大気・水循環保全技術)

In order to control emissions of sodium compounds during coal combustion, the sorbent injection technology is tested under the coal combustion condition. Kaolin is selected as the sorbent to absorb vapors of sodium compounds evolved from the coals. In the combustion experiments, the kaolin is physically mixed with coal. Two types of coal, which have the similar coal properties, are burned. Combustion tests are conducted, using an electrically heated drop tube furnace, to study effect of kaolin addition on the capture characteristics of sodium compounds. As a result, the kaolin can effectively capture the vapor of sodium compounds even under the actual coal combustion condition. The capture efficiency depends on the coal type. The sodium compounds for the coals, which produce many fine particles with size of less than 1μm, tend to be effectively captured by the kaolin.

Control of mercury emissions from coal-fired power plants: a preliminary cost assessment and the next steps for accurately assessing control costs

Mercury emissions from coal-fired power plants have been extensively evaluated for nearly 10 years to determine possible regulation by the Environmental Protection Agency (EPA). Under a court order, a determination will be made on whether it is appropriate and necessary to regulate toxic air pollutant emissions (focusing on mercury) from coal-fired utility boilers by December 15, 2000. If it is determined that regulations are necessary, then the regulatory process will have a fixed timetable. A proposed regulation will be due no later than December 15, 2003, and promulgated no later than December 15, 2004. The utility industry regulatory compliance must be in place by December 2007 since the Clean Air Act requires that sources come into compliance with Maximum Achievable Control Technology (MACT) 3 years after promulgation of the regulations. While it is recognized that the main driver for regulation is the potential risk to human health and that this risk is currently being examined by a number of health-based organizations, the actual form of any regulation would likely be dependent upon the availability of cost-effective control technologies. Furthermore, the diverse nature of the coal-fired utility industry will likely limit the applicability and cost-effectiveness of any given technology for the current boiler population. In light of a potential regulatory determination, this paper examines a few control options that warrant further consideration. A preliminary assessment of mercury capture technologies and associated costs is conducted for sorbent injection technology. Sorbent-based technologies that may be amenable for mercury control include: (1) sorbent injection with and without spray cooling upstream of existing particulate control devices (i.e., electrostatic precipitators and fabric filters); and (2) sorbent injection with and without spray cooling associated with additional control devices designed to augment particulate collection in a primary particulate control device. Important design criteria for each of the control systems are critically assessed for operability, maintainability, and reliability, with the projected impacts of the control system on power plant operations being evaluated. The sorbent-based technology discussed in this paper focuses on the injection of activated carbon associated with the various particulate control devices used in the utility industry. The paper also addresses the next steps and revisions needed to accurately assess possible cost impacts to the utility industry as the mercury control options mature in their development.

Add-on control techniques for nitrogen oxide emissions during municipal waste combustion

Throughout history, man has disposed of ‘municipal solid waste’ via incineration and landfilling. As the population and waste generated per capita increased, and concomitantly the available landfill space diminished, the favored and sometimes only waste disposal option was incineration. Air pollution is one of the costs society bears for incineration. Municipal waste combustion liberates acid gas emissions such as SO x , HCl, and NO x . Flue gas scrubbing and alkaline sorbent injection technologies are typically used to neutralize acidic, SO x and HCl emissions. Staged combustion and more frequently add-on, ‘post-combustion’ control technologies are used to reduce nitrogen oxide emissions. This section of the journal will cover the use of ‘add-on control technologies’ for reducing nitrogen oxide emissions from municipal waste incinerators. A detailed technology description along with process benefits and limitations are discussed. Finally, a generic economic analysis and a list of post-combustion NO x control applications are enclosed.

Advanced coolside desulfurization process

AbstractThis paper describes a dry sorbent injection SO2 abatement process with the potential to significantly enhance desulfurization performance over that of existing in‐duct injection technology such as the Coolside process. The Advanced Coolside process was developed by CONSOL Inc. and is being tested in a pilotscale project, partially funded by the U.S. Department of Energy (DOE). The goals of this process development effort are to increase the applicability of sorbent injection technology as a compliance option for coal‐fired boilers for the 1990 Clean Air Act Amendments and to reduce total process SO2 control costs. Specific performance objectives are to achieve 90% SO2 removal and 60% sorbent utilization efficiency, while retaining the low‐capital cost and retrofit advantages inherent to in‐duct sorbent injection technology. The Advanced Coolside process concept involves flue gas humidification to near the adiabatic saturation point combined with fly ash removal using a gas/liquid contacting device, followed by injection of a sorbent (e.g., Ca(OH)2) into the highly humid flue gas with collection by the existing particulate collector. High SO2 removal and sorbent utilization efficiency are possible with hydrated lime when the flue gas is nearly saturated with moisture. Sorbent utilization is further improved by recycle, and the potential for improvement by the use of recycle is increased with removal of the fly ash before sorbent injection. Further, testing indicates that pre‐treatment of the recycle sorbent before reinjection can improve process performance. Because flue gas is humidified completely before sorbent injection, the existing duct configuration may not limit process retrofit potential. The heat of reaction between SO2 and Ca(OH)2 heats the flue gas before the existing particulate collector. Current pilot test data indicate that the Advanced Coolside process performance objectives are achievable. On‐going process development work includes design optimization for the contacting device, improving efficiency of sorbent recycle, and optimization of sorbent performance.

Sorbent/urea slurry injection for simultaneous SO2/NOx removal

AbstractThe combination of sorbent injection and selective noncatalytic reduction (SNCR) technologies has been investigated for simultaneous SO2/NOx removal. A slurry composed of a urea‐based solution and various Ca‐based sorbents was injected at a range of temperatures and reactant/pollutant stoichiometries. Testing on a natural gas pilot‐scale reactor with doped pollutants achieved up to 80% reduction of SO2 and NOx at reactant/pollutant stoichiometric ratios of 2 and 1, respectively. SO2 emission reductions from slurry injection were enhanced compared with dry Ca(OH)2 sorbent injection methods possibly due to sorbent fracturing to smaller, more reactive particles. Emissions from NH3 slip and N2O formation were reduced in comparison with others' published results while similar NOx reductions were obtained. The injection of the urea‐based solution enhanced the SO2 removal, likely due to the formation of a (NH4)2Ca(SO4)2•H2O compound. The results of this pilot scale study have shown high reduction of both SO2 and NOx, suggesting the need for full scale studies to further assess this combined sorbent/urea‐based slurry injection technology.

Sorbent/Urea slurry injection for simultaneous SO2/NOx removal

The combination of sorbent injection and selective noncatalytic reduction (SNCR) technologies has been investigated for simultaneous SO2/NOx removal. A slurry composed of a urea-based solution and various Ca-based sorbents was injected at a range of temperatures and reactant/pollutant stoichiometries. Testing on a natural gas pilot-scale reactor with doped pollutants achieved up to 80% reduction of SO2 and NOx at reactant/pollutant stoichiometric ratios of 2 and 1, respectively. SO2 emission reductions from slurry injection were enhanced compared with dry Ca(OH)2 sorbent injection methods possibly due to sorbent fracturing to smaller, more reactive particles. Emissions from NH3 slip and N2O formation were reduced in comparison with others' published results while similar NOx reductions were obtained. The injection of the urea-based solution enhanced the SO2 removal, likely due to the formation of a (NH4)2Ca(SO4)2•H2O compound. The results of this pilot scale study have shown high reduction of both SO2 and NOx, suggesting the need for full scale studies to further assess this combined sorbent/urea-based slurry injection technology.

Characterization of Gas Reburning-Sorbent Injection Technology By-Products

ABSTRACTThree samples of fly ashes from pilot-scale tests of gas reburning and sorbent injection (GR-SI) technology were characterized physically, chemically, and mineralogically. Texturally, the samples consist of approximately 97% by weight of silt-size particles. Total chemical analysis showed that Al, Ca, C, Fe, Si, and S were the major elements, making up 56% of the total mass of the sample on average. Approximately 3% of the sample mass consisted of the elements Cl, Mg, P, K, Na, and Ti, and 0.4% consisted of trace elements. Major crystalline compounds found in these samples were lime (CaO), anhydrite (CaSO4), and calcium carbonate (CaCO3). Calculations show that these compounds constituted from 56 to 76% of the mass of the samples. The morphology and chemistry of particles in GR-SI samples were similar to those of particles in conventional coal fly ashes. The particles in the GR-SI samples consisted of fragments and spheres of varying sizes. Most of the particles were calcareous. Silicate and alumino-silicate particles were fewer in number, and iron-rich particles were rare. The EP test indicated that extract concentrations of Ag, As, Ba, Cd, Cr, Pb, and Se were well below the EPA regulatory levels. Predictions of leachate compositions from these types of fly ashes, if disposed of as a landfill at a midwestern U.S. site indicate, that during the first ten years the concentrations of Ca, SO4, Na, B, and OH would remain high. The concentrations of minor constituents (As, Ba, Cd, Cd, Cu, Cr, Fe, Ni, and Se) in the leachate are predicted to be at trace levels.

Pilot process variable study of coolside desulfurization

AbstractThe Coolside desulfurization process is a dry sorbent injection technology developed for retrofit SO2 control in coal‐fired utility power stations. The process is low in capital and space requirements since, in its ideal configuration, the existing ductwork and particulate collector are used as the SO2‐sorbent reaction spaces. It has been developed through laboratory and 1 MW‐scale field tests using hydrated lime as the primary process sorbent by Consolidation Coal Company (Consol). The field work showed promising results with observed SO2 removal ranging up to 80%. In order to optimize the process performance through improved understanding of the process fundamentals, Consol constructed and is operating a 0.15 MW pilot test unit. This paper describes the results of a process variable test program, a first series of tests made in the pilot unit, and the unit operability observed during the test work.