Environmental Engineering Reference
In-Depth Information
Dependable capacity:
The load-carrying ability of a station or system under adverse
conditions for a specified period of time.
Depleted resources:
Resources that have been mined, including coal recovered, coal
lost in mining, and coal reclassified as sub-economic because of mining.
Depletion factor:
Annual percentage of depletion of the thermal resource.
Design head:
The achieved river, pondage, or reservoir surface height (forebay ele-
vation) that provides the water level to produce the full flow at the gate of
the turbine in order to attain the manufacturer's installed nameplate rating
for generation capacity.
Designated wilderness area:
An area designated by Congress as part of the National
Wilderness Preservation System.
Desired future condition:
The qualities of an ecosystem or its components that an
organization seeks to develop through its decisions and actions.
Desulfurization:
The removal of sulfur, as from molten metals, petroleum oil, or
flue gases.
Diesel fuel:
A fuel composed of distillates obtained in petroleum refining opera-
tion or blends of such distillates with residual oil used in motor vehicles.
The boiling point and specific gravity are higher for diesel fuels than for
gasoline.
Diffusive transport:
The process by which particles of liquids or gases move from
an area of higher concentration to an area of lower concentration.
Digester gas:
Biogas that is produced using a digester, which is an airtight vessel or
enclosure in which bacteria decomposes biomass in water to produce biogas.
Diode:
A solid-state device that acts as a one-way valve for electricity.
Direct methanol fuel cell (DMFC):
A type of fuel cell in which the fuel is methanol
(CH
3
OH) in gaseous or liquid form. The methanol is oxidized directly at
the anode instead of first being reformed to produce hydrogen. The electro-
lyte is typically polymer electrolyte membrane (PEM).
Direct use:
Use of geothermal heat without first converting it to electricity, such as
for space heating and cooling, food preparation, industrial processes, etc.
Displacer:
A body moved by the waves. It might be a buoyant vessel or, as in the
case of oscillating water column (OWC) devices, a mass of water. If buoy-
ant, the displacer may pierce the surface of the waves or be submerged.
Distillation unit (atmospheric):
The primary distillation unit that processes crude
oil (including mixtures of other hydrocarbons) at approximately atmo-
spheric conditions. It includes a pipe still for vaporizing the crude oil and a
fractionation tower for separating the vaporized hydrocarbon components
in the crude oil into fractions with different boiling ranges. This is done by
continuously vaporizing and condensing the components to separate higher
boiling point material. The selected boiling ranges are set by the process
scheme, the properties of the crude oil, and the product specifications.
Distributed generation (distributed energy resources):
Refers to electricity pro-
vided by small, modular power generators (typically ranging in capacity
from a few kilowatts to 50 megawatts) located at or near customer demand.
District heating:
A type of direct use in which a utility system supplies multiple
users with hot water or steam from a central plant or well field.
