Vendors often publish sizes and dimensions for different volumetric flow
rates. The dimensions are used in preparing general arrangement drawings.
Typically, to ensure availability, as well
as process flexibility, two 100 percent
capacity mixer systems, or three 50 percent capacity mixers are recommended.
For discharge piping, two 100 percent
discharge pipes are also required. Other configurations are possible, depending on Client requirements or special
load constraints. For example, when
the load changes in a wide range and
the slurry rheology does not allow for
wide control range, two different sizes
of discharge piping and/or smaller mixers can be installed to ensure proper
operational flexibility. Designs must
include provisions for purging pipe and
ensuring that the gypsum/flyash mixture will not solidify in the pipe for any
operating conditions, including black
plant / power failures.
OBTAINING A QUOTE,
PRELIMINARY P&ID, AND
Equipment suppliers normally have
their own quotation data sheets that
will list the type of process data needed
to size and cost their equipment. It is
important to state the major objective
of the system, for example: landfilling
all gypsum, flyash, and wastewater;
landfilling some gypsum and some
flyash (selling some flyash). Also,
important is understanding how the
power plant unit (or units) is operated.
Flyash, gypsum slurry, and waste are
mixed simultaneously in the mixer.
It should be noted that there are cer-
tain limitations as to the relative quan-
tities of the individual CCRs within the
mixer, such as:
• Some flyash is always required,
because this is the reactive compo-
nent that enables stabilization.
• A minimum amount of fine particles are required (fly ash, gypsum,
Installation of two of four fly
ash/gypsum slurry mixers.
Photo courtesy: NAES
less than 160 microns) to provide
the proper viscosity and suspension of larger particles.
• The relative ratios of flyash, bottom ash, and gypsum are not chosen arbitrarily.
PRELIMINARY OPEX AND
The capital expenditure (CAPEX) of
core technology for a 90 gpm (450 MW
power plant burning PRB coal) mixer
system (excluding piping to landfill)
is approximately $1.5 million (U.S.
2015), and includes 2 x 100 percent
mixers (one operating, one standby),
pumps, instruments & control sys-
tem, valves, VFD drives. Installed cost
is about 1. 3 to 1. 5 times the capital
cost, or about $2.1 million (this is for
maximum use of modularization. For
larger mixers, which must be installed
in buildings, and / or bottom ash must
be dewatered, the capital cost multipli-
er would be about 2 to obtain installed
cost. An average would be 1. 8). For
different capacities use a 0.5 exponent
on ratios of volumetric rate; e.g., total
installed cost (turn-key) at 352 gpm is
$1.5M× 1. 8×(352/90)^0.5 = $5.4M. Size
discharge piping for standard carbon
steel pipe for a maximum flow rate of
10 ft/sec; assume 81 lb/ft3 slurry den-
sity. A typical slurry pump train max
discharge pressure is 435 psig. For a
pressure drop in the pipe, use schedule
80 pipe with a relative roughness fac-
tor for old pipe. A 100 percent spare
discharge pipe is recommended. For
cold climates, smaller insulated pipe is
recommended. Typical piping costs of
$600-$800/ton are used. Schedule 80
uninsulated pipe that is nominal 3” in