Firing process

The basic principle in turning a paste with high plasticity into a hard and durable material is connected with dehydration at room temperature most of the absorbed water is already lost from the surface of the crystals. At a few hundred degrees, the water trapped between the layers is removed and later, structural OH groups are attacked. By thermal analysis it could be shown that 

Ceramics can be classified by considering the firing temperature and the resulting porosity thus high-fired stoneware (produced at above 1000°C) has porosities less than 2% and low-fired earthenware (firing between 600 and 900°C) with far more than 10% porosity are at the upper and lower ends of the scale. Porcelain (defined as white and translucent ceramic, fired up to 1400°C) can exhibit an extremely low porosity, whereas terracotta or raku (both fired below 1000°C) would be examples of high porosity. 

Various types of kilns evolved during the history of ceramic production fired brick walls were constructed for field kilns in contrast to periodic kilns, serving only for a limited production campaign round or tunnel kilns provide different features concerning the duration of the firing cycle or the temperature uniformity. A kiln with an oxygen-deficient atmosphere produces harder ceramics (and a different colour) than a kiln with an oxidising atmosphere. 

---

Firing. A hot-air oven having forced circulation in a countercurrent mode is used to dry the fermented tea leaves and inactivates the key enzymes required for fermentation. The firing process generally occurs over an 18—20-min period, which is optimum for normal process efficiencies. 

Combustion. See Sec. 9, Heat Generation and Fired Process Equipment. For incinerators, see material under these subsections. 

Fired heaters differ from other indirect-fired processing equipment in that the process stream is heated by passage through a coil or tubebank enclosed in a furnace. Fired heaters are classified by function and by coil design. 

The three-phase firing process ancient Greek potters used to create this vase utilized both oxidation and reduction processes. 

A flame could begin with the reactants mixed (premixed) or reactants that might diffuse together (diffusion flame). Generally, a flame is thought of with the reactants in the gas phase. Variations in this viewpoint for a flame or fire process might occur and are defined in special terminology. Indeed, while flame applies to a gas phase reaction, fire,... 

Up to now we have only considered prescribed reactions. Given a reaction, the tools of thermodynamics can give us the heat of combustion and other information. In a combustion reaction we could impose conditions of chemical equilibrium, or ideally complete combustion. While these approximations can be useful, for actual fire processes we must rely on experimental data for the reaction. The interaction of turbulence and temperature variations can lead to incomplete products of combustion. For fuels involving CxHyOz we might expect that... 

The indirect-fired process gasifies biomass at low pressure, using indirect gasification to produce gases with medium... 

Dry chemical agents currently used are a mixture of powders, primarily sodium bicarbonate (ordinary), potassium bicarbonate (Purple K), monoammmonium phosphate (multipurpose). When applied to a fire they cause extinguishment by smothering the fire process. They will not provide securement of a flammable liquid spill or pool fire and it can re-flash after it is initially suppressed if an ignition source is present (i.e., a hot surface). Dry chemical is still very effective for extinguishment of three dimensional flammable liquid or gas fires. It is nonconductive and therefore can be used on live electrical equipment. 

The heat accumulation in the bed surface layer causes the ignition of the char combustion process. The heat is supplied from the over-fire process (see Figure 58C). When the char combustion process commenced, the macroscopic ignition front sustains itself with heat from the exothemic oxidation reactions. Large amounts of the heat released by the char combustion zone are also conducted and radiated away both upwards and downwards in the bed. The downward propagation rate of the macroscopic ignition front is controlled by several factors, such as biofuel moisture content, primary air rate and air temperature [33]. The temperature of the macroscopic propagating char combustion zone is around 1000-1200°C in batch-bed combustion of solid biofuels [38,41]. 

Fired process heaters and boilers, incinerators, flares, and other equipment with flame burners are located at an appropriate distance from high value operating or processing areas, large volume storage of flammable or combustible materials, control rooms, operating offices, and their occupants. 

At least one potassium bicarbonate dry chemical extinguisher (120-B C) should be provided at each fired process heater handling liquid fuel or a liquid process stream. They should be installed on opposite sides, or ends, and adjacent to fire aisles. 

---