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Circulating fluidized bed – Wikipedia

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.

The Circulating Fluidized Bed (CFB) is a developing technology for the combustion of coal to achieve a lower emission of pollutants. Through this technology , up to 95 percent of the pollutants [1] can Be absorbed before being emitted into the atmosphere. Introduction

The circulating fluidized bed is a relatively new technology with the ability to achieve a lower emission of pollutants. Extensive research on this technology has been carried out over the last 10 years because pollution in the world is becoming more serious by the day and clean practice will be very crucial to the sustainability of the land. The importance of this technology has recently grown due to the more stringent environmental regulations for the emission of pollutants.

The Mercury and Toxic Air Standards (MATS) promulgated in December 2011 by the EPA have forced all countries in Europe and America to strictly comply with this policy. This means that emissions such as metals, acid gases, organic compounds, flue gas acids and other pollutants from power plants or industrial facilities must meet the requirements set by the EPA. [2] and updates need to be made to Facilities that do not meet standards. As a result, the demand for circulating fluidized bed technology will be predicted to sky rocket.

The industrial application of fluidized bed began long ago. In 1923, the Winkler coal gasifier represented the first significant large-scale use of fluidized bed. [3] (Kunii and Levenspiel, 1991). Today, the largest CFB unit in the world has operated since 2009 in Lagisza, Poland, 460 MW supercritical CFB, Foster and Wheeler. Although cheap liquid and gaseous fuels have slowed coal and solid fuels R & D; Many sectors increasingly use CFB viz. Generation of electricity and industrial sectors, due to the advantages of CFB. The cries of 1970 again reactivated the interest in solid fuel and coal. On the other hand, the growing concern of GHG , the cheap cost of coal and Its abundant sources Motivate again the investigations of CFB (IEA-CIAB, 2013). The CCS was considered as an important technology to mitigate GHGs . To apply CCS, new techniques namely. Precombustion, post-combustion and oxy-combustion. Subsequently, the R & D is carried out to understand the effects of new operating conditions such as the use of gaseous mixture compared to conventional units. This chapter is dedicated to the detailed review of the literature in the fields of hydrodynamic behavior of CFB, oxy-fuel combustion and generations of oxy-fuel combustion. The literature on low or zero carbon (biofuel) energy sources is also analyzed. The special focus on the use of biofuels for CFB is the service of lower or zero carbon energy technology.

Flow regimes and classification
Fluidization is the phenomenon whereby solid particles are transported in a fluid state through the suspension in a gas or liquid. In fact, there is a simple and accurate way of classifying the different beds of fluid particles (Winaya et al., 2003, Souza-Santos, 2004, Basu, 2006). Most of the operational and environmental characteristics of the BFC are the direct results of hydrodynamic behavior. Numerous researchers have studied the hydrodynamics of CFB (Yang, 1998, Basu, 2006, Rodas, 2008, Scala, 2013). Fluidization is a function of several parameters such as the shape, size and density of particles, gas velocity, bed geometries, etc. Kunka and Levenspiel (1991), Oka and Dekker (2004) and Souza-Santos (2004) defined the fluidization regimes described below:

a) Fixed Bed : When the fluid passes through the bottom of the bed at a low flow rate, the fluid simply filters through the voids between stationary particles.
When the velocity of the gas reaches the minimum fluidization velocity, and all the particles are suspended by the fluid flowing upwards.

c) bubble liquid bed : when the flow rate increases beyond the minimum fluidization velocity, the bed begins to bubble. The gas-solid system shows large instabilities with bubbling and gas channeling with increased flow velocity beyond minimal fluidization. Said bed is called aggregate, heterogeneous, or fluidized bubble.

When the gas flow rate increases sufficiently, the terminal velocity ( tr ) of solids is exceeded. The upper surface of the bed disappears, the drag becomes appreciable instead of bubble up,
With an increase in gas velocity, the solids are carried out from the bed with the gas making a poorly fluidized phase, this regime is used to operate CFB. In the present work, the fast fluidized bed is used to operate the BFC where the pressure drop decreases drastically in this regime.

f) Pneumatic transport : beyond the working regime in circulating fluidized bed, there is the pneumatic transport region, the pressure drop increases in this regime.
A contribution appreciated by Geldart (1973) classified particles based on size and density into four groups viz. C, A, B and D. The group B (particle size sub

between 40-500 μm s <1400 kg/m 3 ) is commonly used for CFB. Yang modified the Geldart classification using Archimedes Ar, under high pressure, temperature and non-dimensional density (Yang, 2007).

Pressure and Pressure Drop The flow in a CFB is multiphase. The loss of unrecoverable pressure along the height of the riser is a basic value for the design; And this is due to the distribution of solid particles, vacuum, gas viscosity, gas velocity, gas density and solid density. [4] [5]

Bases of technology

During the combustion phase, upward air jets will cause the suspension of solid fuels. This is to ensure that gas and solids are mixed turbulently for better heat transfer and chemical reactions. The fuel will burn at a temperature of 1400 ° F (760 ° C) to 1700 ° F (926.7 ° C or <> Sup> C) to prevent the formation of nitrogen oxide. [1] While burning, the combustion gases like sulfur dioxide will be released. At the same time, sulfur-absorbing chemicals such as limestone or dolomite will be used to mix with the fuel particles in the fluidization phase, which will absorb almost 95% of sulfur contaminants.
Alternatively, the sulfur-absorbing chemical and fuel will be recycled to increase the efficiency of producing higher quality steam as well as reduce the emission of pollutants. Therefore, it will be possible to utilize circulating fluidized bed technology to burn fuel in a much more environmentally friendly method as compared to other conventional processes.
Application Range

Circulating fluidized bed technology can be implemented in many different fields ranging from oil and gas to power plants. This technology is highly sought after due to its numerous benefits. Some of the popular applications of the circulating fluidized bed are the circulating fluidized bed washer and the circulating fluidized bed gasification system.

One of the applications of a circulating fluidized bed purifier is in power plants using a dry sorbent usually Ca (OH) 2 to reduce contaminants such as HF, HCL, SO 2 And SO 3 in a flue gas stream. Basin Electric Power Cooperative is the only company that operates the best technology.

Of circulating fluidized bed washes available for a coal boiler near Gillette Wyoming since 2011. [7]

The three main components of the circulating fluidized bed purifier in power plants are:

  • Circulating Fluidized Bed Absorber
  • Screen Filter
  • Dry lime hydration system.

In the circulating fluidized bed washing process, the flue gases will enter the reactor from the bottom of the vessel. Simultaneously, the hydrated lime will be injected into the circulating fluidized bed absorber so that the reaction takes place to convert SO 2 and SO 3 of the flue gas into calcium sulphate and sulphite calcic. Water will also be injected at the same time to control the operating temperature for maximum absorption capacity. The flue gas will be sent to the house of the bag for later filtration. In the baghouse, a series of air valves through the filters will produce compressed air bursts to ensure a more efficient collection of solids and dust. Finally, clean flue gases will be directed to the stack with minimal contaminants in the flue gas stream.