N.H. Code Admin. R. Env-Wq 716.07

Current through Register No. 25, June 20, 2024

Section Env-Wq 716.07 - Anaerobic Sludge Digestion: Piping and Appurtenances

(a) Digester systems shall be equipped with thermometers to monitor temperatures of the sludge, hot water feed, hot water return and boiler water.

(b) All portions of the gas system, including the space above the tank liquor, storage facilities and piping, shall be designed such that under normal operating conditions, including sludge withdrawal, the gas shall be maintained under positive pressure.

(c) All occupied enclosed areas where gas leakage might occur shall be mechanically ventilated in accordance with the NFPA as incorporated by reference in the state fire code in Saf-C 6000.

(d) All gas metering, compressor, control and appurtenant equipment shall be located in a separate room with only an outside entrance and equipped with a hazardous gas detection alarm system.

(e) Pressure and vacuum relief valves and flame traps together with automatic safety shut-off valves shall be provided.

(f) The gas piping system shall be:

(1) Protected from freezing;

(2) Sloped 1-2 percent to drain to condensation traps at all low points;

(3) Equipped with either float-controlled or U-tube water seal type condensate traps;

(4) Corrosion resistant; and

(5) Designed to maintain digester gas velocities less than 12 feet per second.

(g) Gas burning boilers and engines shall be:

(1) Located in ventilated rooms at ground level;

(2) Separated from the digester gallery; and

(3) Equipped with flame traps and pressure relief valves at a minimum.

(h) Cogeneration system design parameters shall include:

(1) Volume of gas produced by digesters;

(2) Digester gas energy value in BTUs/cubic foot;

(3) Gas composition;

(4) Gas storage capability; and

(5) Gas pretreatment requirements.

(i) Electrical systems and equipment shall comply with the NEC requirements adopted by reference in the state building code pursuant to RSA 155-A:1, IV, for the installed locations.

(j) Digester pipe galleries shall be designed in accordance with the NFPA as incorporated by reference in the state fire code in Saf-C 6000.

(k) Waste gas burners shall be accessible and located:

(1) At least 25 feet away from any plant structure when placed at ground level; or

(2) On the roof of a control building if they are:

a.Removed from the tank; and

b.High enough that flames will not be blown within 10 feet of the roof surface.

(l) A gas meter with by-pass shall be provided to measure total gas production, per-tank gas production, and flared gas.

(m) Digestion tanks shall be insulated to minimize heat loss.

(n) Sludge shall be heated by circulating the sludge through external heaters and piping shall be designed to provide for the preheating of feed sludge before introduction to the digesters. Provisions shall be made in the layout of the piping and valving to facilitate cleaning of these lines.

(o) Where digestion gas is used for heating, an auxiliary fuel shall be provided.

(p) For tanks where supernatant is withdrawn from the digester, digester supernatant piping shall be:

(1) Not less than 6 inches in diameter;

(2) Arranged so that withdrawal can be made from 3 or more levels in the tank; and

(3) Equipped with an unvalved emergency overflow designed to prevent sludge discharge to the gas system that will convey digester overflow to the WWTP headworks, the aeration process, or to another liquid sludge storage facility and that has provisions for monitoring overflows and sounding an alarm if and when an overflow occurs.

(q) Provision shall be made for sampling at each supernatant draw-off level.

(r) High pressure backwash facilities shall be provided for the piping system.

N.H. Code Admin. R. Env-Wq 716.07

Adopted byVolume XXXIV Number 46, Filed November 13, 2014, Proposed by #10693, Effective 10/15/2014, Expires10/15/2024.