mech13.txt

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     Office of Air Quality, Permitting & Enforcement Division

               Mechanical Section Policy Memorandum

                 

Date:  April 11, 1994                          No.: 13

From:  Mechanical Team

Approved by:  Gary Wallin, P.E. 

Subject:  Concrete Batch Plant Standard Exemption Curves

                  

Policy:   

The emission rates curves titled Concrete Batch Plants,
Standard Exemption Emission Rates, are provided for review of
concrete batch plant standard exemptions.  These are included
with in the Guidance Document for Standard Exemptions No. 71
and No. 93.  The reviewer can determine if a specific concrete
batch plant exceeds the 25 tons per year limit specified in
Regulation VI, Rule 116.211.  The curves can give a quick, but
approximate order of magnitude of an annual emission rate for
a facility given an annual production rate (Yd3/year). 

Although the curves were developed using conservative
parameters, as noted with the document, the reviewer is
responsible for evaluating each application and determining
whether a facility meets the emission requirements of the
exemption.

Background:   

The concrete batch plant curves were developed to provide a
quick reference for determining whether a facility exceeds the
25 tons per year emissions limit.  The curves will expedite
the review of the exemption application and eliminate the need
for the reviewer to calculate the emissions when the facility
operates within the specified parameters.

Necessary Action:  

The reviewer should compare their specific plant type against
one of the three methods ("A", "B", or "C") represented by the
curves.  If the annual emission rate identified from the
proper curve is less than 25 tons per year, then no further
calculations are required.  The reviewer may enter the annual
emission rate as less than 25 tons per year on any
documentation that requires an emission rate.  A copy of the
curve and assumptions should be included in the file.  Anytime
the reviewer is in doubt as to whether the plant's annual
emission rate meets the 25 ton criteria, actual calculations
should be accomplished.

                    Concrete Batch Plant 

              Emission Calculation Assumptions 
                for Standard Exemption Graphs

For "A", "B", and "C" curves:

Given:

Reference:  TNRCC Concrete Batch Plant Standardized Emission
Calculation Instructions (Section III)

Curve "A":  Central Baghouse Method of Calculations.
Curve "B":  Method 1 Vent Style Baghouse Calculations.
Curve "C":  Method 2 Vent Style Baghouse Calculations.

Based on total annual production rate (Yd3/year). 
Maximum wind:  12.4 miles per hour.
Drop point moisture content:  Four percent.
Truck drop control factor:  0.30.
Aggregate drop point control factor:  1.0 (Dry)
Eight drop points for sand.
Eight drop points for aggregate.

For "A" Central Baghouse Curve:

Central Baghouse:  4000 cubic feet/minute.
Outlet Grain Loading:  0.02 grains/dry standard cubic foot
(gr/dscf).
Weigh hopper and truck drop vent to central baghouse.

For "B" Method 1 Curve:

Three individual silos (2 x cement, 1 x weigh hopper).
Silo and Weigh Hopper Baghouses:  350 cubic feet/minute.
Outlet Grain Loading:  0.02 gr/dscf.
Water ring used for the truck drop.

For "C" Method 2 Curve:

Two individual silos (1 x cement, 1 x weigh hopper).
Silo and Weigh hopper baghouses:  95 percent efficient.
(BACT for new and modified baghouses requires 99.5%).
Water ring used for the truck drop.

Please see the attached wordperfect file MECH13.WPG for the
concrete batch plant curves that are a critical part of this
memo.  

cc:  All Mechanical Section                    Added 4-20-94