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Blue Gas
Blue gas is a mixture of gases and consists predominantly of carbon monoxide and hydrogen formed by action of steam on hot coal or coke. The mixture has a tendency to burn with a blue flame, hence the name of the gas.
See also: Blue Water Gas, Carbureted Blue Gas.
Blue Water Gas
Blue water gas (sometimes referred to as blue gas) is produced in a similar manner to produce gas but allows the production of a higher heat content gas by intermittent blasting the incandescent bed with air and steam such that the overall heat balance is maintained. The products of the air blast contain the nitrogen which reduces heat content of the product gas.
The process follows the similar principles to the production of producer gas with the exception that the problem of nitrogen dilution is overcome. The feedstock bed is simultaneously blasted with air followed by steam – the air reaction is exothermic causing the bed to increase in temperature, and this is balanced by the endothermic reaction of the steam. The typical composition of the product gas is on the order of carbon dioxide 5% v/v, carbon monoxide 41% v/v, hydrogen 49%, v/v, methane 1% v/v, and nitrogen 4% v/v. If oxygen is used instead of air, the process can be continuous and coke is preferred to coal because coal can continue to devolatilize in the blow period thereby reducing process efficiency – there are also issues related to process efficiency that arise from the use of caking coal as the feedstock.
The blue water gas may be enriched by adding a carburetor in which heavy (high density, high-boiling) fuel oil is sprayed into a brick lined chamber during the blow period of the blue water gas plant with air. During the make period, the air is turned off and the oil is cracked into smaller hydrocarbon derivatives in the now-heated chamber. This produces a mixture of hydrocarbon derivatives (predominantly methane) which increases the heat content and enriches the gas product.
See also: Blue Gas.
Boiler Slag
Boiler slag is a by-product produced from a wet-bottom boiler, which is a special type of boiler designed to keep bottom ash in a molten state before it is removed. These types of boilers (slag-tap and cyclone boilers) are much more compact than pulverized coal boilers used by most large utility generating stations and can burn a wide range of fuels and generate a higher proportion of bottom ash than fly ash (50 to 80% w/w bottom ash compared to 15 to 20% w/w bottom ash for pulverized coal boilers). With wet-bottom boilers, the molten ash is withdrawn from the boiler and allowed to flow into quenching water. The rapid cooling of the slag causes it to immediately crystallize into a black, dense, fine-grained glassy mass that fractures into angular particles, which can be crushed and screened to the appropriate sizes for several uses.
There are two types of wet-bottom boilers: (i) the slag-tap boiler and (ii) the cyclone boiler. The slag-tap boiler burns pulverized coal, and the cyclone boiler burns crushed coal. In each type, the bottom ash is kept in a molten state and tapped off as a liquid. Both boiler types have a solid base with an orifice that can be opened to permit the molten ash that has collected at the base to flow into the ash hopper below. The ash hopper in wet-bottom furnaces contains quenching water. When the molten slag comes in contact with the quenching water, it fractures instantly, crystallizes, and forms pellets. The resulting boiler slag, often referred to as black beauty, is a coarse, hard, black, angular, glassy material.
Since boiler slag is angular, dense, and hard, it is often used as a wear-resistant component in surface coatings of asphalt in road paving. Finer-sized boiler slag can be used as blasting grit and is commonly used for coating roofing shingles. Other uses include raw material for the manufacture of cement and in colder climates; it is spread onto icy roads for traction control. Because there are so many uses and such a limited supply, most of the boiler slag produced in the United States is used and some even imported from other countries.
See also: Ash, Biomass Ash.
Boiling Water Reactor
A boiling water reactor (BWR) is a type of light (H2O and not HDO or D2O in which hydrogen has been replaced by deuterium) water nuclear reactor used for the generation of electrical power.
The steam in boiling water reactor is produced directly in the reactor core, while, in contact, the steam in a pressurized water reactor (PWR) is produced in a secondary system. The pressure of a pressurized boiling reactor varies from the primary system to the output steam, while the pressure of a boiling water reactor remains constant.
An advantage of the pressurized water reactor is that the pressurized water reactor can operate at higher temperature and pressure on the order of approximately 315°C (600°F) and 2,400 psi. This provides a higher efficiency than the boiling water reactor.
See: Nuclear Reactor – Boiling Water Reactor.
Bone Dry
The term bone dry when applied to biomass or a biomass product refers to 0% moisture content and refers to (in this context) the biomass being extremely or completely dry. For example, wood heated in an oven at a constant temperature of 100°C (212°F) or above until its weight stabilizes is considered bone dry or oven dry.
Boson
A boson is a particle which carries a force and has a whole number spin (spin is a property of subatomic particles). Bosons carry energy. A photon is an example of a boson as it has a spin of 1 and carries electromagnetism. Mesons are also bosons as they carry nuclear force.
See also: Electron, Nuclear Energy, Photon, Positron.
Bottom Ash
The most common type of furnace in the electric utility industry is the dry, bottom- pulverized feedstock boiler. When pulverized feedstock is burned in a dry, bottom boiler, approximately 80% w/w of the unburned material or ash is entrained in the flue gas and is captured and recovered as fly ash. The remaining 20% w/w of the ash is dry bottom ash, a dark gray, granular, porous solid that is collected in a water-filled hopper at the bottom of the furnace. When a sufficient amount of bottom ash drops into the hopper, it is removed by means of high-pressure water jets and conveyed by sluiceways, either to a disposal pond or to a decant basin for dewatering, crushing, and stockpiling for disposal or use.
Bottom ash is the coarser component of the ash and may comprise a substantial portion of the waste. Rather than floating into the exhaust stacks, it settles to the bottom of the power plant boiler. Bottom ash is not quite as useful as fly ash, although power plant owners have tried to develop options for beneficial use options, such as structural fill and road-base material. However, the bottom ash remains toxic when recycled and can leak heavy metals into the groundwater.
See also: Ash, Biomass Ash, Boiler Slag, Fly Ash.
Bottoming Cycle
The bottoming cycle is a cogeneration system in which steam is used first for process heat and then for electric power production.
