SUBJECTS combustibles

If the fuel is removed or consumed by the subject combustion process, no more fuel supplies will be available for the combustion process to continue and it will cease. In some cases, a fuel is not literally removed from a fire, but is separated from the oxidization agent. Foam suppression methods are good examples where the a barrier is introduced to remove the fuel from the air (i.e., oxidizer). Storage tanks and pipeline fires can use pump-out methods and inventory isolation, respectively, as methods of fuel removal. 

If the fuel is removed or consumed by the subject combustion process, no more fuel supplies will be available for the combustion process to continue and it will cease. In some cases, a fuel is not literally removed from a fire. 

All petroleum energy products, as distinct and dissimilar as they can be, are subjected to the process of flame combustion. It is helpful at this point to bring to mind some definitions and general laws of thermochemistry. 

Gasoline engine equipment such as carburetors, injectors, intake manifolds, valve systems and combustion chambers, are subject to fouling by the fuel itself, the gases recycled from the crankcase, or even dust and particulates arriving with poorly filtered air. Three types of problems then result ... 

Annual Proceedings of the Safety Seminars, Dept, of Defense, Explosive Safety Board, Washington, D.C. International symposia on explosives and closely related subjects are excellent sources of information, ie, international symposia on detonation symposia on combustion symposia on chemical problems connected with the stabiUty of explosives international pyrotechnics seminars symposia on compatibiUty of plastics and other materials with explosives, propellants, and pyrotechnics, and processing of explosives, propellants, and ingredients and symposia on explosives and pyrotechnics Mineral Industy Surveys, U.S. Bureau of Mines, Pittsburgh, Pa. Periodic pubhcations dedicated primarily to explosive studies in Propellants and Explosives Journal of Ha yardous Materials, and apparent consumption of industrial explosives and blasting agents in the United States. 

Knock is caused by unwanted chemical reactions in the combustion chamber. These reactions are a function of the specific chemical species which make up the fuel and the environmental conditions to which the fuel is subjected during the compression and power stroke in the engine. Therefore, both the chemical makeup of the fuel and the engine design parameters must be considered when trying to understand knock. 

Power, Energy, and Drives. Centrifuges accomplish their function by subjecting fluids and soHds to centrifugal fields produced by rotation. Electric motors are the drive device most frequently used however, hydrauHc motors, internal combustion engines, and steam or air turbines are also used. One power equation appHes to all types of centrifuges and drive devices. 

Chemical Properties. Anhydrous sodium dithionite is combustible and can decompose exothermically if subjected to moisture. Sulfur dioxide is given off violentiy if the dry salt is heated above 190°C. At room temperature, in the absence of oxygen, alkaline (pH 9—12) aqueous solutions of dithionite decompose slowly over a matter of days. Increased temperature dramatically increases the decomposition rate. A representation of the decomposition chemistry is as follows ... 

According to the National Board of Fire Underwriters, activated carbons normally used for water treatment pose no dust explosion ha2ard and are not subject to spontaneous combustion when confined to bags, dmms, or storage bins (64). However, activated carbon bums when sufficient heat is appbed the ignition point varies between about 300 and 600°C (65). 

The formation of carbon black in a candle flame was the subject of a series of lectures in the 1860s by Michael Faraday at the Royal Institution in London (23). Faraday described the nature of the diffusion flame, the products of combustion, the decomposition of the paraffin wax to form hydrogen and carbon, the luminosity of the flame because of incandescent carbon particles, and the destmctive oxidation of the carbon by the air surrounding the flame. Since Faraday s time, many theories have been proposed to account for carbon formation in a diffusion flame, but controversy still exists regarding the mechanism (24). 

Luminous Flames Luminosity conventionally refers to soot radiation it is important when combustion occurs under such conditions that the hydrocarbons in the flame are subject to heat in the absence of sufficient air well mixed on a molecular scale. Because soot parti-... 

Metals in the platinum family are recognized for their ability to promote combustion at lowtemperatures. Other catalysts include various oxides of copper, chromium, vanadium, nickel, and cobalt. These catalysts are subject to poisoning, particularly from halogens, halogen and sulfur compounds, zinc, arsenic, lead, mercury, and particulates. It is therefore important that catalyst surfaces be clean and active to ensure optimum performance. 

Once a decision has been made to recover materials and/or energy, process flow sheets must be developed for the removal of the desired components, subject to predetermined materials specifications. A typical flow sheet for the recovery of specific components and the preparation of combustible materials for use as a fuel source is presented in Fig. 25-63. The light combustible materials are often identified as refuse-derived fuel (RDF). 

In water-wall incinerators. The internal walls of the combustion chamber are lined with boiler tubes that are arranged vertically and welded together in continuous sections. When water walls are employed in place of refrac toiy materials, they are not only useful for the recovery of steam but also extremely effective in controlling furnace temperature without introducing excess air however, they are subject to corrosion by the hydrochloric acid produced from the burning of some plastic compounds and the molten ash containing salts (chlorides and sulfates) that attach to the tubes. 

Example The combustion process in large vapor clouds is not known completely and studies are in progress to improve understanding of this important subject. Special study is usually needed to assess the hazard of a large vapor release or to investigate a UVCE. The TNT equivalent method is used in this example other methods have been proposed. Whatever the method used for dispersion and pressure development, a check should be made to determine if any govern-mentaf unit requires a specific type of analysis. 

The thermal efficiency of the process (QE) should be compared with a thermodynamically ideal Carnot cycle, which can be done by comparing the respective indicator diagrams. These show the variation of temperamre, volume and pressure in the combustion chamber during the operating cycle. In the Carnot cycle one mole of gas is subjected to alternate isothermal and adiabatic compression or expansion at two temperatures. By die first law of thermodynamics the isothermal work done on (compression) or by the gas (expansion) is accompanied by the absorption or evolution of heat (Figure 2.2). 

Gas turbines, like other mechanical devices, require inspection, maintenance, and service. Maintenance costs include the combustion system, hot-gas path, and major inspections. (See Chapter 21.) The effect of fuel type on maintenance costs is shown in Table 12-8. A cost factor is shown using natural gas as unity. The cost of maintenance is subject to great variations. Recognizing the great difficulty in establishing expected maintenance costs... 

Many methods have been evolved in recent years for assessing flame retardants and the combustion characteristics of plastics and these have been the subject of comprehensive reviews. " ... 

Collection of combustible waste in appropriate containers (e.g. oily rags/other material subject to spontaneous combustion)... 

While this permits more sensitive and accurate reading of concentrations in the 0-to-10% range, this type of instrument is not sufficiently sensitive to give precise indications of concentrations at the TLV of many toxic gases and vapors. In addition, they lack specificity, do not read directly in TLV units (ppm), and are subject to interferences. All combustible gas and vapor indicators are calibrated by the manufacturer using one specific gas or vapor such as methane, and a calibration curve is provided, in percent LEL, for the calibration gas only. 

The aim of this section is to introduce the fundamentals of incineration, adsorption, absorption, condensation, and biological treatment in order to provide a basic knowledge for the selection of suitable equipment. The waste gas characteristics that play a major role in the selection of gas-cleaning equipment are also considered. A detailed presentation of the theory of combustion, adsorption, absorption, condensation, or biological decomposition required for a complete understanding of the subject is not covered in this section (the theory can be found in the handbooks such as Perry s Chemical Engineers Handbook). 

The work generated by the turbine per unit mass of air after receiving combustion gas of mass (1 +/) and subjected to a pressure ratio of / [ - Aplp)2i)] [(1 - (Aplp)4 ], may then be written approximately as... 

The tubes that are around the flame get most of their heat energs t rom radiation. The tubes in the top of the chamber get their heat from com ec-tion as the hot exhaust gases rise up through the heater and heat ihc process fluid in the tubes. The principal classification of fired heaters relates to the orientation of the heating coil in the radiant section. The tube coils of vertical fired heaters are placed vertically along the walls of the combustion chamber. Firing also occurs vertically from the Hoor of the heater. All the tubes are subjected to radiant energy. 

In this study detailed fault trees with probability and failure rate calculations were generated for the events (1) Fatality due to Explosion, Fire, Toxic Release or Asphyxiation at the Process Development Unit (PDU) Coal Gasification Process and (2) Loss of Availability of the PDU. The fault trees for the PDU were synthesized by Design Sciences, Inc., and then subjected to multiple reviews by Combustion Engineering. The steps involved in hazard identification and evaluation, fault tree generation, probability assessment, and design alteration are presented in the main body of this report. The fault trees, cut sets, failure rate data and unavailability calculations are included as attachments to this report. Although both safety and reliability trees have been constructed for the PDU, the verification and analysis of these trees were not completed as a result of the curtailment of the demonstration plant project. Certain items not completed for the PDU risk and reliability assessment are listed. 

Processes or operations tliat require heating of flanunable materials, liquids, and ordinary combustibles are subject to fires in tliis category. 

Organic combustible substances subject to microbial tliermogenesis (e.g.. Agricultural products such as liay and grain)... 

Environmental consequences of combustion are still a high priority requiring investigation of the chemistry and process effects on the emissions. Effective means of eliminating the pollutants is also a subject of further research. 

Using combustion science to improve perfoiTnance tlirougli design changes and engineenng techniques is an ongoing reseai ch subject. 

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