Office of Air Quality, Permitting & Enforcement Division Mechanical Section Policy Memorandum þÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ Date: April 11, 1994 No.: 13 From: Mechanical Team Approved by: Gary Wallin, P.E. Subject: Concrete Batch Plant Standard Exemption Curves þÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ 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