Minergy Clear Horizons Project, Delray, Detroit, Michigan

Site Background

The Minergy Clear Horizons Project is a replacement method for the disposal of sludge generated by the City of Detroit Wastewater Treatment Plant (WWTP). The WWTP located on a 123-acre site in southwest Detroit at 9300 W. Jefferson, collects and treats residential, commercial and industrial wastewater from Detroit and it's suburbs-78 communities in all, or one-third of Michigan's population1. Currently, the sludge generated from the WWTP is burned in on-site incinerators by the Detroit Water and Sewer Department (DWSD). Incineration of the dewatered sludge occurs in 14 multiple hearth incinerators, six of which are referred to as Complex 1 incinerators with the remaining eight referred to as Complex II incinerators. The Department engages contractors for disposals of the ash produced by incineration of sludge cake and for disposal of excess sludge cake which is not incinerated.

However, these incinerators were built and put into operation in the mid 1960s and an alternate method of sludge disposal is needed. In an effort to seek "more environmentally sound and beneficial reuses for (the City of Detroit's) Solids (i.e., the WWTP sludge) than the traditional disposal methods of incineration or deposit of Solids in landfills," the City of Detroit entered into an agreement with Minergy Detroit LLC. The agreement is for the construction and operation of a sewage sludge incineration/glass aggregate production facility, known as the Clear Horizons Project, and will be located on the former Detroit Coke site.

Historically, the Detroit Coke site has been the location of various batteries of coke ovens beginning in the early 1910's. After the initial series of ovens, three additional coke batteries were constructed at the site including the #4 battery, built in 1968. Operations ceased and the first three batteries were demolished prior to 1980. Until that time, Allied Signal Chemical Corporation operated the plant. Detroit Coke operated the #4 battery for a period of eleven years, beginning in 1980 and ending in September 1991, when the site was finally closed. Detroit Coke Corporation had an interim status treatment, storage and disposal permit under the federal Resource Conservation and Recovery Act (RCRA) to operate various on-site processes. In September 1991, the final battery of coke ovens was shut down and later demolished, leaving the site a brownfield.

Site Description

With grounds of approximately 22 acres, the proposed Minergy Clear Horizons plant will redevelop approximately one quarter of the total Detroit Coke site area. The facility has been designed to take in up to 700,000 wet tons of municipal wastewater sludge annually, primarily from the Jefferson Avenue DWSD wastewater treatment plant.

Using a high-temperature incineration process, Minergy will convert this sludge to glass aggregate, an inert material used in construction and industrial markets. This glass-aggregate product is used in manufacturing ceramic floor tiles, roofing shingle granules, sand blasting grit and other abrasives. Sludges will be brought to the Minergy plant in covered trucks, traveling approximately 1500 feet northeast along West Jefferson Avenue from the DSWD treatment facility. The trucks will be unloaded in a closed garage, with a slight negative pressure in the garage being used to control odors. A pressure imbalance will cause the outside air to flow in through doors when opened; most of the air in the garage will be drawn into the feed air stream for the furnaces. The sludges will then be dried and fed into the glass furnace. All burnable materials in the sludge will be used as primary fuel for the furnace and, along with a small amount of coal as a secondary fuel source and as a process fluxing agent, will heat the furnace to over 2300° F.

Exhaust from the furnace will be sent through pollution control devices where it will be treated by high temperature retention, overfire air, selective non-catalytic reduction, dry scrubbers, and fabric filters before being released to the atmosphere. The inorganic material, metals, and other non-burnable components of the sludge will melt and form a dark, molten glass. The glass will be quenched in water, allowing it to solidify into small pellets. That glass aggregate will then be sold for use in asphalt, shingles, sandblasting media, and other industrial applications.