Cement, Energy and Environment

It is the important to note that these limits were proposed by the EPA to apply during all phases of manufacturing operations, including: start-up, shutdown, and malfunction. This action, if finalized, would set a precedent for requiring compliance with a single standard during normal operations and start-up, shutdown and periods of malfunction. The proposed emission limits are very restrictive. The EPA estimates that these new rules will cost US$340 million to implement and could result in a 10 per cent drop in cement production, though the PCA's analyses indicate that the costs and production impacts will be far greater than that suggested by the EPA. There is widespread agreement that the technology applications and effectiveness assumptions used in the rulemaking are deeply flawed. Industry experts recognize that the standards are simply not achievable. The proposed rule uses a severely restrictive and unnecessary pollutant-by-pollutant approach to develop maximum achievable control technology (MACT) standards. This particular approach looks at each pollutant individually and in isolation from one another and then identifies a control technology to address that specific individual pollutant. The resulting MACT then becomes an amalgam of different technologies that is neither realistic nor feasible. Mercury The location of cement plants is based upon the availability of necessary raw materials, and particularly the principle ingredient, limestone. These raw materials contain not just the necessary ingredients of calcium, iron, alumina and silica, but many other elements naturally bound within that same geologic deposit, including trace elements like mercury. Given the huge volumes of materials that are processed in a typical cement kiln (more than 1.5 million t of raw materials and fuels), even tiny amounts of trace metals, like mercury, quickly approach the proposed emission limits. US cement plants universally use coal and petcoke as their primary fuel. Like any other geological deposit coal also contains trace amounts of mercury. The inherent regional variability of raw materials chemistry resulting from geologic variability cannot be avoided. Relocating a cement plant is no more an option than relocating a city. The EPA states that most, if not all, cement plants will need to install some form of mercury control. Currently, activated carbon injection (ACI ) is viewed by some as the best available technology. After fifteen years of experience with ACI, the utility industry learned that effectiveness of this control technology is very site specific. The control of mercury using ACI poses five particularly trouble some issues, each of which impacts emissions reduction, including: • The species of mercury (elemental vs. oxidized). • Exhaust gas temperature. • Residence time of mercury in air pollution control device. • Type of activated carbon employed . • Physical and chemical properties of the exhaust gas stream. The control of mercury is dependent on: the species or form of mercury (elemental vs. oxidized); the temperature profile (research has shown that mercury capture is indirectly proportional to the flue gas temperature); and the residence time of the mercury within a particulate matter control device (fabric filters enhance the potential for mercury capture by activated carbon by greatly increasing the residence time between the mercury and the activated carbon particle. The control of mercury is also dependent on the type of ACI used. Some systems require modifications, such as: more expensive treated carbons or enhancement agents, changing the process to lower the flue gas temperature, replacing electrostatic precipitators (ESPs) with a fabric filter or adding a fabric filter after an existing ESP. Finally, mercury control is dependent on the flue gas compositions itself. All these issues point to expensive strategies including one or more of the following: • Installation of a polishing baghouse. • Use of treated carbons or enhancement agents. • Changes in the strategies for handling CKD. • Installation of a wet scrubber. • Evaluation and testing of more experimental types of mercury control technologies. Unfortunately, none of these strategies is a guarantee that ACI will achieve compliance for mercury control at many cement plants. Some point to the wet scrubber technology for mercury control. That is not feasible. It is well known in the utility industry that oxidized mercury captured in a wet scrubber can be re– emitted as elemental mercury! 34