MACT Task Force

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# Memorandum

To: Jeff Telander, EPA
From: Garth Tayler: Acme Brick Company
Date: June 23, 2010
Re: Discussion of why there are no HF and HCl emissions for brick plant dryers

BACKGROUND

There is a concern that certain amount s of HF, HCl and particulate matter may be emitted from the dryer stacks of clay brick oper ational processes. The purpose of this memo is to discuss t he design and operation of the brick drying and firing system and to explain why the emission of HAPs and PM from the dryer stack is highly unlikely with a corre ctly designed and o perated clay brick tunnel kiln/dryer system.

DESIGN FEATURES OF THE TUNNEL DRYER/KILN SYSTEM

Extruded clay brick that are set onto kiln cars, pass through the tunnel dryer to bring the moisture down to less than 1%, pr ior to firing. The firing process takes place through the tunnel kiln, which is designed to heat up the brick load gradually through the various stages in or der to develop the desired fired color and required degree of vitrification to render it durable and fit for purpose.

The typical tunnel kiln firing process is made up of the following stages:MACT Task Force

2 | Page 1. Kiln exhaust section; cons isting of exhaust ports, ducting and
exhaust fan. 2. Early pre-heat zones; consisting of burner and/or recirculation
sections to maximize the convec tive heat transfer process. 3. Main pre-heat zones; utilizing co nvective and radiant heat transfer to facilitate oxidation and load preparation for the final high temperature firing stage. 4. Furnace zones; designed to devel op the final vitrification and color development of the material. 5. Rapid cool zone; the load is cooled rapidly down to the quartz inversion temperatur e of approximately 1100  F. 6. Ware cooling zone; the load is gradually cooled to final exit temperature.

In order to maximize efficiency and energy recovery, the tunnel kiln is designed with a heat recovery scheme that extracts thermal energy from the ware and the kiln cars via a hot air recovery system in the rapid and ware cooling sections of
the kiln. These sections are connected to the drying process and are the cooling sections (stages 5 and 6) of the tunnel kiln. This part of the kiln operates independently of the firing z ones of the kiln. Between it and the firing zone is an
area of the kiln known as a neutral zone.

This area is a virtual area of the kiln wher e the pressure balance on either side is
such that no air movement occurs thr ough this area. Subsequent to a pressure balance scenario some kilns also use the quick cooling air supply volume to
create an air curtain to further insure t hat airflow occurs as required. Downstream of the neutral zone (with respect to airflow as in towards the kiln exhaust zone) is where the combustion gasses and any off gassing from the brick body travel, along the length of the t unnel to the exhaust section.MACT Task Force

3 | Page The ware, moving through the tunnel, passes through the preheating and final firing zones and into the above mentioned cooling zones, where cooling down takes place under controlled conditions. Ambient air is drawn into the exit and intermediate parts of the cooling section. This ambient air cools the mass of the load; the resulting heated air is drawn from the kiln by means of a centrifugal fan and transported through a ducting system to the dryers. This design ensures that no products of combustion or HAPs emissions are present in the waste heat circuit supplying the dryer air when the co rrect operation of the kiln is taking place.