Boiler Flue Gas Research Articles

Fundamental Research and Demonstration Project of Evaporation Treatment of Wastewater from FGD in Flue Gas Duct

The desulfurization wastewater is a kind of intractable wastewater which comes from the process of wet desulfurization. There are many shortcomings of traditional development methods. Desulfurization wastewater evaporation treatment in flue gas duct as a new processing technology. This approach of evaporating desulfurization wastewater by flue gas is feasible. The feasibility of the demonstration project of boiler flue gas treating wastewater on 4# boiler in Changshu Power Company limited was analyzed; the computational fluid dynamics (CFD) software FLUENT was adopted to simulated the pressure field and velocity field in the outlet flue pipes of air pre-heater. The concrete arrangement mode and the number of the spray lances were determined by calculations. The temperature of the flue gas is tested after the system was put into operation. The results showed that this technology can realize the desulfurization wastewater with zero discharge without hurting the work of electrostatic precipitator. The demonstration project is the first of its kind in domestic power industry; this study provides experiences and references of power plant desulfurization wastewater with zero discharge.

Energy Efficiency Improvement through Technology Optimisation and Low Grade Heat Recovery – Industrial Application

Small and Medium-sized Enterprises (SMEs) form the backbone of national economies and especially of the food industry, which in Ireland is made up of over 90 % SMEs. These foods related SMEs have very similar structures, usually containing a small or medium boiler, ovens, chillers, heat exchangers and an extended water network. Another common characteristic is the low energy efficiency due not only to the relatively small size of equipment but also to the non optimisation of the heat network and substantial waste heat and effluent emissions. Therefore, it is an excellent environment to apply system analysis, process integration and optimisation methods, waste heat recovery and waste emission reduction technology with expected high economic and environmental impacts. In this paper the opportunities for energy efficiency improvement with the example of a medium-sized company which produces sliced cooked meats are presented. For this purpose a complex analysis of the heat network is carried out using guided redesign of the technology based on Process Integration, improving the internal heat exchange in order to increase and consequently to minimise the exit exergy (available useful heat) reducing the energy supply. Additionally the application of an advanced technology for boiler flue gas low grade heat recovery with preliminary humidification of the combustion air using waste heat is proposed. As a result an overall efficiency improvement of 20-25 % (respectively less fuel consumption and carbon emission reduction), about 68 % water consumption and effluent reduction and up to 3.8 times less NOx gas emissions is estimated.

Experimental Study on the Spray of Mercury Removal Performance of Flue Gas Desulfurization Wastewater

For coal-fired power plant boiler flue gas desulfurization wastewater’s actual spraying proposed combination bag house dust while mercury removal process. Experimental study of the coal-fired boiler flue gas spraying chlorine ions and other halogens desulfurization wastewater modified fly ash flue gas mercury performance. Studies showed that desulfurization wastewater fly ash on chloride ion enhanced oxidation of elemental mercury, with the increase in the amount sprayed desulfurization wastewater, flue gas mercury capacity increased. Desulfurization wastewater add another halogen element can promote flue gas mercury performance, the effect of iodine was the most significant, followed by bromine. The desulfurization wastewater as a modified liquid sprayed into the flue modified fly ash, fly ash can improve mercury removal performance, eliminate the need for desulfurization wastewater treatment, cost savings, achieve desulfurization wastewater recycling.

Pilot Plant Studies on Nox Removal Via No Ozonation and Absorption

Abstract The results of experimental investigations on the removal of NOx from gases applying ozone as the oxidizing agent and the absorption of higher nitrogen oxides in the sodium hydroxide solutions are presented. The experiment was conducted using a pilot plant installation with the air flow rate 200 m3/h, being a prototype of a boiler flue gas duct and a FGD scrubber. It was shown that in the range of [NOref] = 50 ÷ 250 ppm the mechanism of NO ozonation depends on the molar ratio X = O3/NOref: for X ≤ 1.0 oxidation of NO to NO2 predominates and NO2 is poorly absorbed, for X >> 1.0 NO2 undergoes further oxidation to N2O5, which is efficiently absorbed in the scrubber. The stoichiometric molar ratio of complete conversion of NO into N2O5 is X = 1.5, in these studies to reach the effectiveness η ≥ 90% the molar ratio X was much higher (2.75).

Microwave assisted vacuum regeneration for CO2 capture from wet flue gas

Small scale processing of flue gas with the goal of enriching the stream in CO2 for sequestration or use is an interesting application area for adsorption technology. For example, boiler flue gas which may contain up to 10 % (v/v) CO2 in air can be readily enriched to a stream containing >70 % CO2 which may be ideal for use within a process such as acidification, precipitation, stripping, etc. The challenge in these applications is producing high purity CO2 without excessive energy use and handling high concentrations of water vapor without the added complication of a pre-drying stage. In this study we have examined the use of microwave assisted vacuum as a way of rapidly directing thermal energy to the adsorbent surface to liberate water and CO2. Preliminary “proof-of-concept” pump down experiments were conducted on a small transparent adsorption column of 13X zeolite pre-saturated with a 12 % CO2 in N2 gas mixture. Both wet and dry gas tests were conducted. The addition of microwave radiation improved the rapid desorption of CO2 and water and improved the integrated CO2 purity in the blowdown stream from 60 to 80 %. In the case of dry CO2 mixtures, the enhancement is due to microwave heating of the 13X zeolite facilitated by the high cation density in the faujasite structure. In the case of water and CO2 desorption, the temperature rise of the adsorbent upon microwave heating was much lower than that predicted by simple heating suggesting that the microwave radiation is absorbed primarily by the adsorbed water. A simplified energy analysis suggests that brief exposure of an adsorbent to microwave radiation will raise the required vacuum level for regeneration of high humidity flue gas streams and may lead to an overall lower energy penalty. The selective ability of microwave radiation to target different species provides scope for optimized, compact, flue gas treatment systems.

Experimental Investigation of CO<sub>2</sub> Separation from Lignite Flue Gases by 100 cm<sup>2</sup> Single Molten Carbonate Fuel Cell

The paper presents an experimental investigation of using a Molten Carbonate Fuel Cell (MCFC) for reducing CO2 emission from the flue gas of a lignite boiler. The MCFC is placed in the flue gas stream and separates CO2 from the cathode side to the anode side. As a result, a mixture of CO2 and H2O is obtained; from which pure CO2 can be obtained by cryogenic condensation of water and carbon dioxide. The main advantages of this solution are: additional electricity generated, reduced CO2 emissions and higher system efficiency. The results obtained show that the use of an MCFC could reduce CO2 emissions by 90% with over 30% efficiency in additional power generation.

Numerical Simulation of O<sub>2</sub>/CO<sub>2</sub> Pulverized Coal in 300MW Boiler

O2/CO2combustion technology is an effective method to capture and store coal-fired boiler flue gas CO2. With a 300MW subcritical pulverized coal boiler as the research subject investigated, Fluent numerical simulation software is used to simulate the process of pulverized coal combustion both in air and O2/CO2conditions. The comparative analyses are made both in the former conditions, such as the combustion characteristics of pulverized coal, the influence of oxygen volume fraction, the effect of the secondary air temperature on the temperature field in the furnace of pulverized coal boiler. As for the following results of the pulverized coal combusted in the O2/CO2condition, compared with the results in the air condition, its time of ignition is delayed, and the combustion temperature is low and the central position of flame rises. With the increasing percentage of the oxygen volume and the rising temperature of secondary air, the time of ignition speeds up, which improves the overall furnace temperature level and transferring capability of the radiation heat.

Techno-economic analysis and optimization of the heat recovery of utility boiler flue gas

Coal-fired power plants in China consume nearly half of available coals, and the resulting CO2 emissions cover over 40% of total national emissions. Therefore, reducing the energy expenditure of coal-fired power plants is of great significance to China’s energy security and greenhouse gas reduction programs. For coal-fired power plants, the temperature of a boiler’s exhaust gas reaches 120–150°C or even higher. The thermal energy of boiler’s exhaust accounts for approximately 3–8% of the total energy of fuel input. Given these factors, we conducted a techno-economic analysis and optimization design of the heat recovery system using boiler exhaust gas. This research is conformed to the principles of thermodynamic, heat transfer, and hydrodynamics. Based on the data from an existing 1000MW typical power generation unit in China, four typical flue gas heat recovery schemes are quantitatively analyzed from the thermodynamics perspective. The impacts of flue gas heat recovery on net work output and standard coal consumption rate of various schemes are performed. Furthermore, the transfer area of heat recovery exchanger and the draft fan work increment due to the flue gas pressure drop are analyzed. Finally, a techno-economic analysis of the heat recovery schemes is conducted, and some recommendations on optimization design parameters are proposed, with full consideration of various factors such as the decrease on fuel cost due to energy conservation as well as the investment cost of heat recovery retrofitting. The results revealed that, high-stage steam substitute scheme of flue gas heat recovery in power plant can obtain higher energy-saving effects than that of low-stage steam substitute scheme. And the energy-saving benefit of flue gas heat recovery, especially with high-stage steam substitute scheme, is weakened by large heat exchange areas and flue gas pressure drop caused by lower temperature differentials. Therefore, the techno-economic performance of the flue gas heat recovery in power plant may not always increase with the increment of the recovered heat but have an optimum point.

Pilot-scale multistage membrane process for the separation of CO2 from LNG-fired flue gas

In this study, a multistage pilot-scale membrane plant was constructed and operated for the separation of CO2 from Liquefied Natural Gas (LNG)-fired boiler flue gas of 1000Nm3/day. The target purity and recovery of CO2 were 99vol.% and 90%, respectively. For this purpose, asymmetric polyethersulfone (PES) hollow fibers membranes has been developed in our previous work and has evaluated the effects of operating pressure and feed concentration of CO2 on separation performance. The operating and permeation data obtained were also analyzed in relation with the numerical simulation data using countercurrent flow model. Based on these results, in this study, four-staged membrane process including dehumidification process has been designed, installed, and operated to demonstrate the feasibility of multistage membrane systems for removing CO2 from flue gases. The operation results using this plant were compared to the numerical simulation results on multistage membrane process. The experimental results matched well with the numerical simulation data. The concentration and the recovery of CO2 in the permeate stream of final stage were ranged from 95–99vol.% and 70–95%, respectively, depending on the operating conditions. This study demonstrated the applicability of the membrane-based pilot plant for CO2 recovery from flue gas.

A New Activated Carbon for CO2 Capture from Coal-Fired Boiler Flue Gas

With the current environmental interest in controlling greenhouse gases, there is a new focus on materials that can discriminate between gas molecules by capturing those gases that must be curtailed and releasing those that pose no adverse effects to the atmosphere. Although zeolites can be applied to such tasks, molecular sieve (MS) carbons have an additional advantage in their ability to both adsorb and desorb molecules cyclically with comparatively little energy demand. ATMI's BrightBlack™ MS carbons have been extensively characterized using a variety of techniques and modified for the task of selectively adsorbing CO2 from a synthetic flue gas in a laboratory and a pilot plant falling-bed adsorber system. The integrated falling-bed adsorber system was then moved to a field test location to capture CO2 from flue gas from a coalfired stoker boiler. In a 7000-cycle test, the carbon captured CO2 at 90% efficiency, generating product CO2 gas with purity greater than 95%.

Desulfurization of boiler flue gas by means of activated calcium oxide

The research including two sorbents produced by the activation of quicklime, transforming calcium oxide into calcium hydroxide and calcium carbonate proved by means of a reactor with a static layer that temperature significantly limits their chemisorption reactivities during the capture of sulfur dioxide from boiler flue gas from coal combustion and biomass co-combustion or sorted municipal flues and brown coal. An increased desulfurization reactivity was demonstrated with a product with a lower hydroxide and higher carbonate content. Its sorption activity was proven to be significantly higher at 110°C than at 130°C and 150°C. The desulfurization was getting stronger with the decrease of the difference of Sorbacal application temperature to the dew point of flue gasses.

Studying the removal of nitrogen oxides from boiler flue gases in firing natural gas

Basic statements relating to the mechanism through which nitrogen oxides are oxidized and absorbed in the course of purifying flue gases using a new comprehensive method are presented together with versions used for implementing the purification process. The results obtained from tests of a pilot commercial installation are given, and its performance indicators are estimated.

The Carbonation Behaviors of Limestone Particle in Oxygen-Fuel Circulating Fluidized Bed O<sub>2</sub>/CO<sub>2 </sub>Flue Gas

Limestone powder is still applied as SO2 sorbent in emerging oxygen-fuel circulating fluidized bed boiler, but its carbonation in O2/CO2 flue gas is an unclear problem. For a better understanding of carbonation behaviors, the tube furnace heating system was built for simulating circulating fluidized bed boiler flue gas by regulating the supply of O, CO2, N2, SO2 and H2O, and Carbonation reaction was tested. Thermal gravimetric analysis and scanning electron microscopy were used. It was found that carbonation is closely related to temperature, CO2 concentration, impurities, water vapor, and cycle times; high temperature can promote carbonation process; high concentration of CO2 can inhibit the chemical reaction stage speed of carbonation process, but it has little effect on the final conversion rate; water vapor can increase the final conversion rate of carbonation; the cycle times will reduce the activity of carbonation. The presence of carbonation turns the traditional boiler flue gas indirect desulfurization model into indirect desulfurization mechanism which does not have a negative impact on SO2 removal efficiency.

Thermodynamic analysis of pre-drying methods for pre-dried lignite-fired power plant

Lignite is considered to be a competitive energy raw material with very high security of supply viewed from a global angle. However, the utilization of raw lignite faces many thorny issues, such as a low plant thermal efficiency, a high investment in construction of the lignite-fired power plant, etc. Lignite pre-drying seems to be an attractive way to tackle these issues. We have performed a thermodynamic analysis of two pre-drying methods (both boiler flue gas drying and steam drying). Results show that both pre-drying methods can improve the plant thermal efficiency. Nevertheless, the boiler flue gas drying improves the plant thermal efficiency only in the case when the temperature of the dryer exhaust is low enough and the dryer thermal efficiency is high enough. The steam pre-drying has a higher potential in plant thermal efficiency improvement. The flow rate of steam extraction for the steam dryer is much lower than the flow rate of flue gas extraction for flue gas dryer, so we consider that the steam pre-drying is more appropriate for the revamp of the conventional lignite-fired power plant. In addition, we have calculated and analyzed main factors.

The Analysis on Energy Saving Reconstruction of a Grade III-A General Hospital in Wuhan

Take one of Grade III-A general hospitals in Wuhan as the research object with auditing the hospital's energy consuming system. It can be proved that the energy consumption per unit area is 27kgce/m2 , analysis of typical of the hospital exterior envelope, lighting systems, central heating and air conditioning system for hospital energy, gave priority to recycle the boiler flue gas heat and condensation water, natural light using, exterior windows transforming and installation of the sub-metering systems for energy saving renovation. The comprehensive transformation energy-saving rate is 31.71%. Energy saving quantity is 318.01tce. A total investment is 4.3948 million yuan. The payback period is 2.5 years.

Theoretical prediction of sulfuric acid condensation rates in boiler flue gas

Prediction of acid condensation has a critical role in designing heat exchangers to recover water vapor from power plant flue gas. Rates of mass transfer for condensation of sulfuric acid vapors onto heat exchanger tubes were theoretically investigated and a computer program for numerical simulations of sulfuric acid (H2SO4) condensation in a flue gas condensing heat exchanger was developed. Governing equations based on mass and energy balances for the system were derived to predict variables such as flue gas exit temperatures, cooling water outlet temperatures, and molar fractions and condensation rates of water and sulfuric acid vapors. The associated equations were solved using an iterative solution technique and a one dimensional finite difference method with forward differencing. The Controlled Condensation Method (EPA Method 8B) was applied to experimentally obtain concentration profiles of sulfuric acid vapor in flue gas along downstream in the system. Predicted results of sulfuric acid vapor condensation were compared with empirical data for model validation, and the discrepancy is analyzed in terms of measurement and computation uncertainties. It is found that from both modeling and test results sulfuric acids as well as water vapors are reduced and separated in condensing heat exchanger due to mass transfer with condensation in flue gas. The modeling methodology described here is applicable to theoretical prediction of sulfuric acid and water condensation in full scale flue gas condensing heat exchanger applications.

Silica-Titania–Coated Packing: Novel Solution Capable of 90% Hg Capture with Low Operation and Maintenance Costs

A silica–titania composite (STC) material has been commercialized for mercury removal from caustic exhaust at a U.S. chlor-alkali facility employing a mercury-cell process. A second-generation STC, applicable to larger flow rates such as those associated with coal-fired boiler flue gas, was developed and evaluated for this study. This new material, consisting of high void space chemical tower packing dip coated with an STC formula, was named Silica-Titania–Coated Packing (STCP). The STCP was capable of 90% oxidation and removal of mercury from a simulated flue gas under conditions where other technologies would fail. Additionally, a preliminary cost estimate determined that the STCP would have much lower average annual costs than two commercial technologies that are widely accepted as the best available for this application.

A dechlorination pathway for synthesis of horn shaped carbon nanotubes and its adsorption properties for CO2, CH4, CO and N2

Using metallic copper as reductant and tetrachloroethylene as carbon precursor, a simple, low temperature solvothermal method for the synthesis of horn shaped carbon nanotubes is reported. The detail study of reaction parameters such as temperature, time, carbon precursor amount, type and catalyst proportion has been carried out to optimize the conditions wherein that the copper metal (10g) mediated reduction of tetrachloroethylene (25mL) at 200°C for 5h resulted in the horn shaped carbon nanotubes with high yield and structural selectivity. The adsorption properties of horn shaped carbon nanotubes were investigated for carbon dioxide, methane, carbon monoxide and nitrogen as adsorbate by volumetric measurements up to 850mmHg. The prepared horn shaped carbon nanotubes showed good adsorption capacity for CO2 (45cm3/g) and CO (17cm3/g), at 303K and 850mmHg pressure, with high equilibrium selectivity (73.3 for CO2 and 110.7 for CO at 318K) and capacity selectivity (9.1 for CO2 and 3.1 for CO at 850mmHg and 318K) over nitrogen which provides the tool for the separation of CO2 from its mixture with nitrogen observed in flue gas of thermal power plants and boilers, as well as with CO such as syngas.

Pilot Investigation on Mechanical Stirred and Pneumatic Drying of Bagasse with Boiler Flue Gases

A novel system of mechanical stirred and pneumatic drying of bagasse with boiler flue gases was developed and experimented on pilot scale in a sugar mill. Investigation was performed on factors affecting the dried bagasse moisture content, the drying efficiency of the dryer, and the pressure drops of both the dryer and the separating cyclone. Optimal operating conditons were found to be stirring speed 40 rpm, throughput of the pilot dryer 1000 kgh-1, and flow rate of flue gases 4500 kgh-1. The pressure drops of the dryer and the cyclone were less than 100 Pa and 250 Pa respectively. The novel system was superior to conventional dryers on both the drying efficiency and the power demand by the induced fan.

Oxidative Removal of Elemental Mercury in Flue Gas by DBD Discharge Plasma

Oxidation of gas phase elemental mercury (Hg0) in the simulated flue gas by DBD plasma under atmospheric pressure and ambient temperature (298 K) was conducted. Experimental results indicated that the oxidative efficiency of Hg0 increased with O2 content, the residence time of flue gas in reactor and the applied voltage. The oxidation efficiency of Hg0 reached over 96% under the applied voltage of 11 kV and the residence time of 0.24 s when the O2 content in flue gas was 20%, and the corresponding energy efficiency was at about 14.1 μg kJ-1. It was noted that the oxidation efficiency of Hg0 could still reach 80% when the O2 content in flue gas was only 4% (near the actual O2 content in flue gas of coal-fired boilers). The experimental results indicated that DBD plasma was one of the efficient technologies for purification of Hg0 vapor industrial flue gas.