impart motion to the sludge. The unit shall effectively transmit the
mixer's mechanical energy to the sludge without producing unbalanced forces
on the shaft. The unit shall be constructed of a material capable of
withstanding rapid motion through sludge without undue wear or corrosion.
[The unit may operate unenclosed or enclosed in a draft tube. The draft
tube shall be flared at the bottom and shall be constructed of at least 6
mm 1/4 inch thick steel plate.] [The propeller shall be designed to avoid
fouling and also to pump sludge in either direction.]
2.4.7
Controls
Each mixer shall be provided with a magnetic starter; forward, stop, and
reverse pushbuttons; and a circuit breaker with manual reset. Controls
shall be [120] [_____] volts ac, single phase, 60 Hz, and shall be housed
in explosion-proof NEMA 250, Type 7 enclosure Reverse operation shall be
provided for periodic dislodging of sludge from the [impeller] [or]
[propeller].
2.5
COMPRESSED GAS SLUDGE MIXING SYSTEM
**************************************************************************
NOTE: Include only the applicable system. Consult
with various manufacturers to determine correct
system for the project and to obtain criteria to be
specified.
For projects with single-stage sludge-digestion,
delete "primary" and include reference to bottom
1/10 of contents. For projects with two-stage
sludge digestion, include "primary" and delete
reference to bottom 1/10 of contents.
**************************************************************************
A system shall be provided for mixing [all except the bottom 1/10] of the
[primary] [_____] digester contents by the circulation of digester gas.
The system shall be designed for safe handling of digester gas. [The
system for each digester shall consist of a compressor, piping system, and
[_____] diffusers located within each digester as indicated. The system
shall provide [_____] cubic meters per second cfm of digester gas at
[_____] kPa psi sequentially to each of the diffusers to provide thorough
mixing of the digester contents.] [The system for each digester shall
consist of a compressor, piping system, and [_____] diffusers within a
centrally mounted draft tube, forming a confined gas lift for circulation
and mixing of the digester contents. The system shall provide a total of
[_____] cubic meters per second cfm of digester gas at [_____] kPa psi to
the diffusers.] [The system for each digester shall consist of a
compressor, piping system, and [_____] diffusers located [on] [near] the
bottom at the center of each digester as indicated, forming an unconfined
gas lift for circulation and mixing of the digester contents. The system
shall provide a total of [_____] cubic meters per second cfm of digester
gas at [_____] kPa psi to the diffusers.]
2.5.1
Compressor
**************************************************************************
NOTE: For gas recirculation and low pressure gas
handling, rotary displacement, sliding vane, or
liquid ring compressors may be used.
**************************************************************************
SECTION 11380
Page 19
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