Perhaps his almost perfectly spontaneous love of small flowers is already a considerable advance over his so-called prototype. Figure 4.1. Spontaneous combustion phenomena occurred in the coal yard. Most chemical accidents have occurred because some of these effects were not foreseen or taken into account, and most research on combustion processes has been conducted to explain unforeseen events and potential hazards. Thermal ignition represents an additional safety risk in combustion processes. Oxygen is a potentially hazardous gas capable of producing violent spontaneous combustion on contact with flammable contaminants such as rust deposits and other degradation products in oxygen pipes, solvents, lubricants and greases. Similarly, the presence of pure oxygen can significantly reduce the ignition temperature of flammable particles. The requirements for oxygen filters are therefore strict and unique and determine the choice of material and the design of the filter body, the choice and shape of the filter element as well as the seals and accessories. Auto-ignition or spontaneous combustion is a type of combustion that occurs by self-heating (increase in temperature due to internal exothermic reactions), followed by thermal runaway (self-heating that accelerates rapidly to high temperatures), and finally spontaneous combustion.
[1] Substances stored in warehouses may be hazardous because they are flammable, flammable, explosive, toxic, corrosive, unstable, reacting with air and/or water, pyrophoric or spontaneously flammable or oxidizing. Given that the problem of dust layer and pile combustion exists in industry, how can these hazards be identified and the resulting risks assessed? One approach is to use graphical techniques such as fault tree analysis (FTA) and event tree analysis (ETA). AFT is a deductive method that identifies specific factors (e.g., fuel, oxidizer, and ignition source) that lead to a general adverse event (e.g., fire). ETA, on the other hand, is an inductive method in which an event (e.g., fire) is further investigated to determine possible outcomes based on the success or failure of various safety measures or barriers (e.g., automatic extinguishing). Fault trees are therefore generally associated with prevention efforts and event trees with mitigation (or protection) efforts. Britannica.com: Encyclopedia article on spontaneous combustion This chapter describes the problems of oxidation and spontaneous combustion in coal storage. Charcoal deteriorates during storage due to oxidation at low temperatures, accentuated by heating, weathering and handling. If the oxidation rate is high and storage conditions are poor, spontaneous combustion may occur. The oxidation rate varies inversely with rank, i.e. the oxidation of highly volatile coals (lower rank) is rapid and the oxidation of highly volatile coals (high rank) is slow. The rate of oxidation also increases with the increase in surface area, i.e. with the decrease in the size of citrus fruits or particles.
Oxidation produces heat that raises the temperature of the coal mass, unless the heat is removed as produced by aeration or other means. Due to difficulties in measuring and interpreting the data, no precise quantitative relationship has yet been established between coal rank and oxidation rate. The most important effect of storage deterioration in the absence of spontaneous combustion is the loss of caking power. Prolonged storage affects coker properties, analyzes gas and tar yields. Spontaneous heating is the slow oxidation of an element or compound that increases the volume temperature of the element or compound without the addition of an external heat source. Spontaneous heating may be the result of direct oxidation of hydrocarbon derivatives (e.g. oils and solvents) or occur due to the action of microorganisms in organic matter. Saturated hydrocarbon derivatives (such as alkane derivatives) do not tend to ignite spontaneously, while unsaturated hydrocarbon derivatives tend to ignite spontaneously. Materials being processed, stored or transported can heat themselves. Self-heating is due to the exothermic reaction of the slow oxidation of the material. When conditions are critical, this self-heating leads to inflammation.
Examples include materials handled in processing equipment such as dryers, materials stored in warehouses or outdoors, or materials transported in large containers such as ships. A well-known example is the spontaneous combustion of coal, which is stored in piles on the ground. Chandra et al. (Chandra et al., 1983) presented conflicting results from the application of different test methods to characterize the spontaneous combustion potential of the same solid. These authors found that two coals characterised by the same CPT differ in their risk profile. As shown in Table 16.21, the samples designated as E and F have the same peroxide value at room temperature, but different crossing point temperatures. In addition, three different coals have the same crossing point temperature, but different peroxide value values. Grinders reduce the coal to a size suitable for combustion. For large boilers and low- or medium-row coals, it is usual to introduce the coal directly into the furnace. For spontaneous combustion to occur, the rate of heat generated by oxidation must exceed the rate of heat dissipation by conduction, convection and (thermal) radiation. When the temperature of the material begins to rise, the rate of heat production often increases. The result is an uncontrolled reaction that eventually causes inflammation.
When the rate of heat dissipation exceeds the generation rate, the material cools and does not ignite. The rate of heat dissipation can be increased by physical contact with a thermally conductive surface, by rotating fuel material stacks to cool hot spots, and by circulating inert gases through the batteries to cool hot spots and move oxygen. Combustion is noticed by an increase in CO measured in the return air pathways, often combined with a characteristic smell of volatile hydrocarbons released as the coal heats up. If not brought under control quickly, spontaneous fires can develop rapidly and lead to catastrophic mining losses. Auto-ignition can be controlled by gradually isolating and sealing all mined areas, blowing nitrogen or other inert gases. For example, exhaust gases from kerosene boilers. If spontaneous combustion is a known hazard, the mine must be constructed so that flood-affected operations can be rapidly flooded with inert gas. Continuous monitoring of all exhaust air flows and rapid response to increased CO are essential to manage the risk of combustion. Haystacks[2] and compost piles[3] can self-ignite due to the heat generated by bacterial fermentation.