Circulating fluidized bed is a relatively new technology with the ability to achieve lower emission of pollutants. Extensive research has been conducted on this technology for the past 10 years because pollution in the world is getting more serious by the day and clean practice will be very crucial for the sustainability of the earth. The importance of this technology has grown recently because of tightened environmental regulations for pollutant emission.
Over the past two decades, CFB technology—including CFB boiler operation and CFB boiler design—has demonstrated its ability to efficiently utilize a wide variety of fuels while still meeting stringent stack emission limits.Our CFB boiler technology allows for a wide range of fuels to be burned efficiently. This includes low-grade and difficult-to-burn fuels such as anthracite, lignite, petroleum coke, oil shale, discarded coal, and biomass within a wide range of mixing rates.Selective non-catalytic reduction (SNCR) systems can be added to our CFB boilers, leading to even lower NOx emissions.
Coal is used as fuel for nearly forty percent of the world’s electricity production (IEA, 2010). This role is expected to continue in the foreseeable future. shows overall coal capacity and age distribution of units, while Figure 1 shows the overall coal capacity and age distribution of the units, while That shows the age distribution and size of the units (Platts, 2011). ).
Figure 1: Global coal power generation capacity and age distribution of units
Figure 2: Distribution of age and size of coal-fired generation units worldwide
At the end of March 2011, the world’s coal-fired power generation capacity was approximately 1,650 GWe, from almost 1,240 GWe in 2006 (Platts, 2011). Pulverized coal technology is the dominant technology for coal-fired power generation at present, with unit sizes of up to 1100 MWe in Europe and China. The majority of new additions to coal capacity (~ 70%) were in China.
Coal-fired Power Generation – Australian Context
In Australia, black and brown coals generate 77% of our electricity (ESAA, 2010).
In 2009-2010, on electricity production of 230,674 GWh, 53% came from black coal and 24.3% came from brown coal.
With a total production capacity of 52,000 MWe, the capacity of the coal-fired power plant was just over 22,000 MWe, while the coal-fired power generation capacity Was a little over 7300 MWe (ABARE, 2011).
Of the total coal capacity (black coal and brown coal), all but 140 MWe were based on pulverized coal technology.
What is the combustion of the circulating fluidized bed (CFBC)
CFBC units use bed materials (such as silica sand) to support the combustion of coal or any solid fuel of about 900 ° C to generate heat. The steam generated inside the combustion chamber can be used to generate electricity in the steam turbines. CFBCs can tolerate variable particle size (micron-sized as in pulverized coal units to a coarse feed size of about ~ 10 mm), variable fuel quality (from anthracite to lignite , Petroleum coke, biomass and opportunity fuels).
The main features and benefits of CFBC are listed in the highlighted area below.
CFBC Features and Benefits
Lower operating temperature, around 900 ° C, compared to the combustion of pulverized coal
Bed materials and coal / coal particles circulating throughout the oven and the high speed return leg, 3-8 m / s
Fuel Efficiency – high-to-low-quality fuels, biomass and opportunity fuels
Uniform Heat Flow
Excellent Next Loading Capacity
In situ capture of sulfur dioxide rather than flue gas desulphurization as in the combustion of pulverized coal and increased calcium use
Lower formation of NO x with respect to combustion of pulverized coal due to lower operating temperature
Improved combustion efficiency due to longer residence time of circulating solids compared to pulverized coal combustion
Less erosive ash compared to the combustion of pulverized coal
Compact boiler size
Simplified fueling, spraying is not necessary, crushing is sufficient
The effectiveness of CFBC units is similar to coal units sprayed under identical steam conditions
High combustion temperatures in coal-fired boilers can cause slag and fouling problems in the furnace, superheater and heater sections depending on the quality of the coal . Therefore, regular soot blowing is necessary to keep these areas clean. On the other hand, the combustion temperature in the CFBC boilers is low, around 900 ° C., which reduces the problems of slag or fouling. Therefore, blowing of soot is not necessary except in low temperature areas such as economizer, primary superheater, airheater (Macdonald, 2006).
A typical schematic of a CFBC-based power generation facility is presented in .
Figure 3: CFBC boiler diagram (Macdonald, 2006)
CFBC Air Technology Status
presents the regional CFBC capacity for energy production purposes, While figure 5 shows the distribution of age and size Of these units (Platts, 2011).
Figure 4: Overall CFBC Power Generation Capacity
Figure 5: Overall CFBC Power Generation Capacity, Unit and Age Distribution of Units
The main points to note in relation to the figures above are as follows:
- CFBC’s total operating capacity – 46,500 MWe at the end of 2010, or about 2.7% of total coal-fired generation capacity. This figure was 17,000 MWe at the end of 2004, or 19,000 MWe at the end of 2008, which represents a significant increase in the new generation of CFBCs in recent years.
- The majority of CFB capacity additions were in China and to a lesser extent in India.
- The largest CFBC to date – Lagisza in Poland, 460 MWe, and supercritical steam parameters (460 MW, 282 bar pressure, 563C superheat reheat temperature / 582C reheat temperature) his genre. It works on Polish bituminous coals. Supplied by Foster Wheeler, the unit was commissioned in early 2009 and exceeded design efficiency by 43.3% (LHV, net) during operation.
- A second 330 MWe supercritical CFR boiler is scheduled for commissioning in 2012 Novocherkasskaya GRES plants in Russia (Platts, 2011).
- The largest CFB (600 MWe) with supercritical steam parameters is under construction in Baima, Sichuan, China.
- Hyundai Energy and Construction Corporation and Korea Southern Power Corporation have commissioned Foster Wheeler 2 x 550 MWe units with supercritical steam parameters to be ordered in 2015. The fuel to be used is bituminous coal and anthracite.
- A major guideline in China’s five-year plan is to build CFB units of more than 600 MW (CEC, 2007).
- Recirculation of the cooled solids from the external heat exchanger allows an Oxy-CFB boiler to operate with lower combustion gas recirculation compared to Oxy-PF systems.
- Reduced flue gas recycling, thus reducing the size of the boiler island and some of the auxiliary consumption. This could potentially allow CFB boilers to be more compact and cheaper.
- Direct sulphation of limestone will occur due to the high partial pressure of CO 2 and the correct thermodynamic temperature for sulfur capture; Calcium conversion under direct sulphation is generally superior to that of calcination / sulphation due to the better porosity of the product layer, as suggested by several studies.
- As also shown in Chapter 3, the transition from combustion in air mode to oxy-mode combustion is potentially easier compared to Oxy-PF, as BFC has a large amount of inert material which Helps control bed temperature.
- Like CFBC & # x27; S are functionally slightly relative to atmospheric pressure, the possibility of an air leakage is considerably reduced.
Timeline for CFBC scaling
shows the timeline for scaling CFBC. Figure 6 shows the timeline for scaling CFBC.
Foster Wheeler offers a supercritical CFB up to 800 MWe for high quality fuels and quot; With a full commercial warranty (Hotta et al., 2010, Jantti and Parkkonen, 2010) for bituminous coal, with steam conditions of 300 bar, a superheater temperature of 600 ° C and a reheat temperature of 620 ° C .
The second generation units (in Figure 6 ) differ from first generation units in Designs that can incorporate supercritical vapor conditions and larger unit sizes, yet in a smaller furnace volume. shows the scaled CFR footprint of 35 MWe in terms of power consumption 1994 to 800 MWe current Design.
However, given the expectation of lower furnace temperatures in general, design improvement will still be required for ultra-supercritical vapor parameters much higher than overheating or reheating temperatures of 600 ° C If these temperatures and the main vapor pressure are reached at 280 bar, these units will achieve a yield greater than 45% (LHV, net) or 43% (HHV, net) for black coal.
Figure 6: CFBC Scale Chronology for Current Operational Units (Utt et al., 2009)
Figure 7: CFBC size at a scale of 35 MWe to 800MWe (Hotta, 2009);
developments from 35 MWe to 110-150 MWe occurred around the same period
Table 1: List of main CFBC functional units for energy generation and their key parameters
Australian context
Of the total Australian coal-fired power generation capacity, only the Redbank power plant has 2 CFN units of 2 x 75 MW (Addinall, 2011). Lignite CRC, now interrupted, had ordered a pilot plant CFBC (350 kWth) from Lurgi and a Victorian brown coal triated and char in 1999-2000.
Although the Australian experience in BFC is limited, global experience has improved considerably. Therefore, for this report, we relied on the experience of major global suppliers and major research institutions.
CFBC Main Sellers
Foster Wheeler
Alstom
Babcock and Wilcox
China
Dongfang and Wuxi Boiler (working with Foster Wheeler)
Harbin / Dongfang / Shanghai Boiler (working with Alstom)
What is Oxy-CFB
Oxy-CFB combustion chambers are CFBC variants, where fluidization and combustion are achieved by a mixture of oxygen and recycled fumes (CO 2 -rich) water). The latter helps maintain bed and gas temperatures at the same level as in an air-supplied CFBC. This is analogous to the Oxy-PF combustion, where the combustion gases are recycled to the burners; In the Oxy-CFB unit, recycled gas can be fed into and around the CFBC bed region.
Oxy-CFB boilers include all the advantages of CFBC technology, such as fuel flexibility and low NOx emissions. Additional benefits of Oxy-CFB include:
Oxy-CFB Benefits
Strong mixing in the furnace and long residence time due to the recirculation of solids allows good carbon depletion; This is clearly appropriate for low-reaction coals.
The oxygen concentration in the recycled combustion gases can be maintained at a low and safe level, while additional oxygen can be introduced through oxygen nozzles separated from the burner, Insertion of secondary gases. Thus, compared to Oxy-PF, Oxy-BFC do not need a new burner design.
Compared to air-CFB, Oxy-CFB is still in development, so not all potentially
Problems are known at the moment.
