Pressurized Fluidized Bed Combustion Systems Research Articles

Experimental investigation on the coal combustion in a pressurized fluidized bed

Pressurized oxy-coal combustion is considered as one of the most promising carbon capture technologies in terms of high carbon capture efficiency and low cost. However, practical operational experience with pressurized coal combustion in a fluidized bed, especially with continuous coal feeding, is still very limited. In this study, a pressurized fluidized bed combustion system was developed and a series of coal combustion experiments were carried out with continuous coal feeding under the pressures from 0.1 to 0.4 MPa. The effects of the combustion pressure and stoichiometric air coefficient on the fluidized bed combustion performances of a Chinese lignite in terms of the temperature distribution profile, apparent solid holdup, combustion efficiency, conversion ratio of carbon in coal to CO2 and ash composition were investigated. The experimental results show that an increase in pressure is beneficial to the improvement of combustion efficiency, and the positive effect of increasing stoichiometric air coefficient on the conversion ratio of carbon in coal to CO2 is more obvious with a lower combustion pressure. The bottom ash and fly ash have similar chemical compositions under different pressures. Based on the experimental data, a correlation as the functions of pressure and stoichiometric air coefficient is proposed to predict the conversion ratio of carbon in coal to CO2.

Biomass co-firing in a pressurized fluidized bed combustion (PFBC) combined cycle power plant: A techno-environmental assessment based on computational simulations

The co-utilization of coal with biomass and biomass waste in a pressurized fluidized bed combustion (PFBC) system is a promising power generation option for addressing various areas of concern relating to the anthropogenic sources of harmful emissions, the global reliance on fossil fuel and the overall energy supply issues. In this study, coal with a wide range of biomass and biomass waste types such as straw, willow chips and switch grass as well as miscanthus and olive pits are fired in an advanced PFBC system. The produced gases and the evolved heat energy are employed to run a combined cycle. To understand the behavior of the proposed system, detailed computational simulations are carried out utilizing various feedstock mixtures ranging from 100% coal to 40% biomass. The results of the simulations are used to show the effect of co-firing on the technical and environmental performance of the power plant. The results show that the main parameters affecting the overall power plant efficiency are the co-firing ratios and the specific properties of the chosen biomass/waste types. Furthermore, the investigation indicates that the steam cycle output reacts more sensitive to the fuel configurations than the gas turbine cycle. As expected, the increased fraction of biomass or waste significantly reduces net CO 2 emissions, and has a beneficial influence on SO x emissions. NO x emissions tend to rise for all biomass types, except the high moisture content willow chips, with increasing co-firing fraction.

実験室規模の加圧流動層燃焼における窒素酸化物の生成特性―チャーによるＮＯｘ分解―

A laboratory scale pressurized fluidized bed combustion (PFBC) system was designed and constructed to clear the details of combustion of coal in PFBC. This PFBC system allows visual observation of hot fluid-ized bed by using a transparent electric furnace. To simulate the emission characteristics of coal combustion of the full scale PFBCs by this lab-scale PFBC, a new similarity rule was introduced. Volumetric heat input and mean gas residence time through fluidized bed in lab-scale PFBC were adjusted to the values matching those of full scale PFBCs. Motion of bubbles and burning of coal particles and volatiles were recognized by visual observations. Volatiles burned mostly in the bottom region of the fluidized bed. On the other hand, char particles burned uniformly in the bed. Ranges of conversion of fuel-N to NO agreed with those obtained in a full scale PFBC. Thus, it is verified that new similarity rule explained above is useful to simulate the combustion behaviors in full scale PFBC by a laboratory scale small PFBC.Effects of operating pressure and O2 partial pressure in flue gas on NO emission were examined. Linear relationship between O2 partial pressure and NO emission was observed. NO emission was decreased rapidly with increasing in operating pressure at constant O2 partial pressure. This may be caused by an enhance-ment of NO reduction by char particles because of increase in number density of char particle in the bed at elevated pressure. In order to confirm this assumption, initial combustion rate of char in the pressurized fluidized bed condition was measured. Initial combustion rate of char increased with 0.6th power of operating pressure. This means that char number density is increased in elevated pressure condition. One of the major reasons to achieve the low NOx emission in PFBC condition, should be the reduction of NOx by char particles through the bed.

Improvement of Strength in Porous Ceramics by Control of Additives

The strengths of porous ceramics are improved by the control of additives with maintaining appropriate porosity, 30∼40vol%. The addition of small amount of CaCO 3 additive improved the strength of porous silicon carbide hot gas filters, which collects the dust particles in the pressurized fluidized bed combustion system. The strength of NiO-10mol%YSZ sintered at 1500°C, which applicable for the anode of SOFC, was higher than that of NiO-8mol%YSZ materials due to the increase in the fraction of intergranular fracture. The result indicates that the additives are one of the crucial factors for the enhancement of strength in the porous ceramics.

Factors affecting the tensile strength of hot-gas filter dust cakes

The University of North Dakota Energy and Environmental Research Center is determining some of the fuel-, sorbent- and operations-related conditions that lead to blinding or bridging of hot-gas particle filters in pressurized fluidized bed combustion systems. Several mechanisms contribute to the stickiness of dust particles within a filter cake: electrostatic and van der Waals attractions, and mechanical, liquid and solid bridging. The magnitudes of these mechanism impacts depend on the size and composition distributions of the dust particles, cake porosity, gas composition and system temperature. High-temperature tensile strength measurements of filter dust cakes have shown that only a small amount of liquid is necessary to double the tensile strength of a cake. The amount of strength increase is related more to the wettability of the dust than to the liquid's viscosity or air-liquid surface tension. Also, if the tensile strength of a filter cake is less than approximately 50 N/m 2, the cake re-entrains after being pulsed off and can lead to blinding of the filters. If the cake strength is over approximately 300 N/m 2, it can bridge between filters, in some cases forcing them apart and causing them to break. However, the factors affecting cake strength are not independent variables and laboratory measurements have shown that the tensile strength of filter dust does not adequately explain its propensity to bridge across filters in a hot-gas filter system. A better measurement is the tensile strength divided by the density of the cake, or its specific strength. The authors have defined the cake specific strength as its critical thickness index (CTI) because it indicates the maximum thickness for which a cake would build before failing or shedding under its own weight. Laboratory measurements show that the CTI is a better indicator of the observed propensity of a particular dust to form bridges between filters than its simple tensile strength.

Materials issues in bubbling PFBC systems

In recent years, considerable experience and insight regarding the behavior of materials and components in the bubbling pressurized fluidized-bed combustion (PFBC) of coal has been developed, largely as a result of the operation of a fleet of 80-MW(e) PFBC-based power plants installed by ABB Carbon. The first plant went into operation over 10 years ago and it appeared timely to review this practical experience and to document areas where improvements have been made, or can be suggested.In keeping with general bubbling-bed experience, the in-bed heat exchanger and water-wall tubes experienced metal loss. Other plant areas that experienced difficulties were the hot-gas cyclone system, the gas-turbine expander, and some balance-of-plant items including solids-handling equipment, valving, and expansion joints. The captured dust removal lines from the cyclones sometimes plugged sending high dust loadings over to the turbine expander. Consequently the turbine blades experienced material deposition and significant erosion damage. Concerns about turbine longevity in this application have led to attempts to develop high-temperature filter systems that protect the turbine by removing all the dust from the flue gas prior to expansion. These filters have themselves suffered from a range of materials problems, which is not unexpected for a relatively new technology. The current experience of these and other materials issues is reviewed.

Predicting the pressure drop across hot gas ceramic filter installed in a commercial size pressurized fluidized bed combustion system

Predicting the pressure drop across hot gas ceramic filter installed in a commercial size pressurized fluidized bed combustion system

Indirect Detection of Nitrogen Oxide Emission on Actual PFBC (Pressurized Fluidized Bed Combustion)

A potential method for evaluating the concentration of gaseous nitrogen oxides in the exhaust gas from the pressurized fluidized bed combustion (PFBC) system was developed, and then its effectiveness was certified in a 71MWe PFBC demonstration plant at Wakamatsu Work, Electric Power Development Co. The total amount of nitrogen oxides (NO, NO2 and N2O) in the exhaust gas was closely related with the N content in the coal used as a fuel and contained no thermal-and prompt-NOx (NO and NO2) originating from N2 in air, due to a low combustion temperature of around 1, 130K in the PFBC system. The concentration of NOx and N2O was estimabed as a function of the temperature and oxygen partial Pressue in the exhaust gas, if burning coal was specified. By pseudo thermodynamic equilibrium over the fluidized bed under the successive supply of the slurry fuel and pressurized air, conversions of N in the fuel coal into NOx and N2O could be expressed by ASHTR-NOx and -N2O equations, respectively, based on the temperature measured by thermocouple and the oxygen partial pressure by a YSZ oxygen sensor. The calculated NOx and N2O concentrations by the equations were well agreed with the measured values by commercially available instruments, demonstrating the potential use of this method for rapid and indirect monitoring of gaseous nitrogen oxides in the exhaust gas from the PFBC system.

97/02172 Prediction and measurements of volatile metal partitioning in coal-fired combustion systems

Power generation using pressurized fluidized bed combustion (PFBC) of coal coupled with combined cycles is a proven high-energy efficiency technology which ensures low environmental impact. Due to the inherent characteristics of PFBC technology, both SOx and NOx emissions can be maintained at low levels. Several demonstration power plants have been constructed worldwide employing PFBC technology. However, PFBC installations are not without their problems, including bed agglomeration, fouling and erosion of the gas turbine blades. Further improvements in efficiency can be achieved through the partial gasification of coal in a carbonizer to produce a fuel gas which is then combusted in a topping combustor (second-generation PFBC systems).

5537941 Pressurized fluidized bed combustion system and method with integral recycle heat exchanger: Goidich Stephen, Palmerton, PA, United States assigned to Foster Wheeler Energy Corporation

5537941 Pressurized fluidized bed combustion system and method with integral recycle heat exchanger: Goidich Stephen, Palmerton, PA, United States assigned to Foster Wheeler Energy Corporation

Coal-Fired CAES System Using Fluidized Bed Combustion

Utility requirements for peaking power can be addressed with coal through the unique marriage of the compressed air energy storage and fluidized bed combustion technologies. This paper discusses the results of an evaluation of a pressurized fluidized bed combustion system at air storage pressures from 27 to 68 atm. A conceptual design of the PFBC configuration in a CAES system is presented. Major components of the system are identified as either state-of-the-art or requiring further R and D. The performance of the compressed air energy storage system with an efficiency of 83.4% (based on coal input energy) is presented. The effects of recovery of rejected heat are discussed also.

A thermogravimetric study of the sulfation of limestone and dolomite — prediction of pressurized and atmospheric fluidized-bed desulfurization

A pressurized thermogravimetric (TG) analysis system was used to study the isothermal reaction of sulfur dioxide with limestone and dolomite at 1 and 10 atm pressure, and temperatures from 750 to 1050°C. Sorbents of 44–4000 μm particle size were sulfated in gases simulating a 10–300% excess air level in a coal combustion atmosphere. The TG rate data were used to predict the desulfurization performance of limestone and dolomite sorbents in atmospheric and pressurized fluidized-bed combustion systems. The projections are compared to available pilot plant data (i.e., the pressurized Exxon miniplant), and their limitations are discussed.