Agglomeration in Stripper Ash Coolers and Its Possible Remedial Solutions: a Case Study

Abstract

The bottom ash of circulating fluidized bed (CFB) boiler contains large amounts of physical heat. When low quality coals are used in these types of boilers, the ash content is normally more than 40 % and the physical heat loss is approximately 3 % if the bottom ash is discharged without cooling. Bottom ash cooler (BAC) is often used to treat the high temperature bottom ash to reclaim heat, and to facilitate the easily handling and transportation of ash. The CFB boiler at BLA Power, Newari, MP (India) is facing problems of clinker formation in strip ash coolers of plant since the installation of unit. These clinkers are basically agglomerates, which leads to defluidization of stripper ash cooler (BAC) units. There are two strip ash coolers in unit. Each strip ash cooler is capable of working independently. The proper functioning of both strip coolers is very important as it is going to increase the combustion efficiency of boiler by stripping of fine unburnt coal particles from ash, which are injected into the furnace. In this paper causes, characterization of agglomerates, thermo gravimetric analysis of fuel used, particular size distribution of coal and sand and possible remedial solution to overcome these agglomerates in strip ash coolers has also been presented. High temperature in compact separators, non uniform supply of coal and not removing small agglomerates from stripper ash cooler are among main causes of agglomeration in stripper ash cooler. Control of compact separator temperature, replacing 10-12 % of bed material and cleaning stripper ash cooler periodically will decrease agglomeration in stripper ash cooler of unit.

Economic impacts of optimizing energy recovery in clinker cooler using clinker cooler bed as a case study

“…Clinker coolers operates on the principle of heat exchanger and fluidization: process of heat exchange between the forward flow red hot clinker leaving the kiln at a temperature of about 1350°C meeting with a upward flow of fresh air at a temperature between 32 and 45°C which leads to cross-flow and the material flow process inside the clinker cooler, this process is known as fluidization (Oyepata et al, 2021;Ahmet and Ahmet 2010). Fluidization is a process by which solid materials are converted into a fluid and causing the materials to be suspended a gas or liquid (Kunii and Levenspiel, 1991;Ravi, 2016). Fluidization occurs when the fluid moved upward via the bed of solid particles (clinker).…”

“…If the fluid flow rate is Source: (Oyepata et al, 2020;Oyepata et al, 2021) sufficient enough the solid particles becomes too fluidized. Fluid with higher flow rates will allows faster movement of the solid particles and all particles (clinker) will be suspended by the fluid, this is known as fluidized bed (Kunii and Levenspiel, 1991;Ravi, 2016). An additional increase in the fluid flow rate can lead to circulation of the fluid in the solid particles inside the vessel and this can also lead to displacement of lighter particles.…”

“…An additional increase in the fluid flow rate can lead to circulation of the fluid in the solid particles inside the vessel and this can also lead to displacement of lighter particles. Fluidization phenomena occurs because a drag forces by the moving gas which is equal to the solid particle weight W p it is known as geostatic pressure) as described in equation (1) (Kunii and Levenspiel, 1991;Ravi, 2016). This process of material fluidization is applicable in clinker grate coolers.…”

“…Therefore, fluid velocity is expressed as a velocity in the free area of the vessel (over or below) the bed of particles. This is known as superficial velocity and expressed in equation ( 2), (Kunii and Levenspiel, 1991;Ravi, 2016).…”