Environmental issues associated with the permitting process for TXI´s modernization of their Midlothian, Texas cement plant

An important step in any expansion project is obtaining an air permit. Obviously, it is quicker to obtain an air permit via the replacement of existing equipment with new modern equipment versus the building of a green-field plant. The shorter permit attainment time is generally linked to the ability to “net out” in emissions. With respect to cement plants, the term “netting out” refers to no increases in emissions of particulate, nitrogen oxides (NO_x ), sulfur oxides (SO_x), and carbon monoxide (CO). TXI chose to evaluate the feasibility of expanding their Midlothian Cement Plant. The purpose of this paper is to discuss the permitting strategy associated with the expansion of TXI Midlothian Cement from 1.2 million stons (1.09 million mtons) of clinker to 2.8 million stons (2.5 million mtons). This permitting strategy led to the replacement of two, 900 sTPD (816 mTPD) long wet kilns with a 6,000 sTPD (5,443 mTPD) modern 4-stage preheater/precalciner kiln without an increase in emissions. In order to “net out” in particulate emissions, state of the art dust collector technology had to be used. Dust collectors for the new plant and part of the existing facility had to incorporate membrane bags in their design. In order to “net out” in sulfur emissions, a wet sulfur scrubber was considered in the design of the new kiln line. In order to “net out” in NO_x emissions, the new kiln line was installed with low NO_x calciner technology. In order to “net out” in CO emissions, a regenerative thermal oxidizer (RTO) with 95% thermal energy recovery was incorporated into the design. It is important to note that this is the first application of RTO technology in a cement plant. The general arrangement of the sulfur scrubber and the RTO is shown