GCI TECH NOTES ©
by
David Gossman
New Portland cement plants being built in the United States are being met by many opponents of using coal as fuel. This effort is being championed and led by the Sierra Club (see http://beyondcoal.org ) primarily against coal burning power plants but new cement plants are getting caught up in this anti-coal campaign. There are a number of reasons why this is a critical error on the part of local activists and their supporters at the Sierra Club. The biggest of these is the fact that this effort will actually increase emissions, especially the greenhouse gas emissions that are a big part of this effort. This action thus falls under the category of “the law of unintended consequences.”
The biggest implied positive impact of using natural gas instead of coal to fuel a cement plant is the potential to decrease CO2 emissions. Nevertheless, this impact is much smaller than the proponents of natural gas are apparently aware. Unlike a power plant, a cement plant does not release CO2 from the coal combustion alone. Over half of the CO2 emitted from a modern cement plant is typically from the calcination of the limestone (calcium carbonate). Calcination is the process that is required as the first of a series of chemical reactions inside a cement kiln needed to make the compounds that make up Portland cement. Because of this, the design of a cement plant to use natural gas instead of coal will only decrease CO2 emissions by less than 25%, assuming that the physical size of the plant stays the same. This value, however, does not take into account the decrease in efficiency that will also result from using natural gas.
In the cement manufacturing process both the raw materials and all of the combustion gases must be contained inside the cement kiln system. Because natural gas produces far more gas molecules from combustion (lots of water molecules and some CO2) to get the same amount of heat, a cement kiln designed to use natural gas to manufacture a fixed amount of cement may need to be physically larger than one designed to use coal. Any physical increase in size decreases thermal efficiency and increases heat loss. It also requires larger amounts of electrical power to power larger kiln drive motors and larger fans to pull the combustion gases through the kiln. Shifting emissions to another location and negatively impacting fuel efficiency is not something that the Sierra Club or their followers should be promoting.
Another claim by those promoting the use of natural gas to manufacture Portland cement is the belief that this will significantly decrease a broad range of other pollutants such as sulfur emission, particulates and toxic metals. This perception is based on their understanding of how power plants work and has nothing to do with cement kilns. The fact is that cement kiln emissions are primarily due to the sulfur, metals and other components of the raw materials used to make Portland cement. The cement manufacturing process operates in a counter-current flow, with the heat from the flame moving upward in one direction and the raw material (primarily ground limestone) moving downward in the other direction. Because of this counter-current flow, coal combustion products such as coal ash and sulfur are actually incorporated into the Portland cement product.
One metal that can be marginally impacted by not using coal is mercury. Half or more of the mercury going into a cement kiln can be from the coal. Yet the fact is that those few cement plants that have major issues with mercury emissions have these concerns because of mercury in their raw materials, not in the coal they use. The simple fact is that the relatively small amount of mercury found in coal is easily dealt with in the cement manufacturing process and rarely causes problems with established strict standards for mercury emissions from new cement plants.
It also needs to be pointed out that use of natural gas to manufacture cement will increase NOx emissions. No matter what control technology is used to limit NOx, emissions from a cement plant using natural gas will still result in an increase when compared to a cement plant using coal and manufacturing the same amount of cement. This is caused by the higher flame temperatures that are associated with natural gas use. NOx emissions from a cement plant are almost entirely from thermal NOx. Increase the flame temperature and NOx goes up, it is that simple. Further, natural gas use produces that impact automatically. Does the Sierra Club really want to promote increasing ozone-forming NOx emissions for a very small decrease in CO2?
It may be the case that the Sierra Club and others can force utilities to make higher priced electricity with natural gas instead of coal. The simple fact is that there is a captive market and the electricity really does need to be generated relatively close to where it is used. The same is not true for Portland cement. If opponents are successful in preventing a cement plant using coal from being built that does not mean that one using natural gas will be built. Quite the opposite, it simply means that the coal fired cement plant will be built somewhere else, very likely overseas in a developing country. If that is the intent of the Sierra Club and their supporters they need to be honest about it and look closely at those consequences. Here they are:
Globally, CO2 emissions will increase well beyond that of locally produced cement. Why? Because there will be increased CO2 emissions related to transportation. Actual increases in CO2 emissions will be in the range of 10-20%.
Other pollutants will increase. Why? Again transportation has a big impact but let’s not pretend, those developing countries are not going to require the level of advanced control and monitoring of emissions that are required here in the US. Further, mercury emissions, the one hazardous air pollutant that might decrease based on natural gas use, is a global emission issue. Cement plants in developing countries do not have any limits on mercury emissions, thereby likely resulting in significantly increased global mercury emissions.
Environmental Justice Communities will be more severely impacted. Clearly those developing countries often have what would be classified in the US as minority and low income communities where these plants would be located. How can the Sierra Club promote a policy that actually promotes environmental injustice just because it is outside of the United States?
Finally, let’s not forget jobs. It is a well established fact that the higher the standard of living in a nation or a community, the more attention is paid to environmental issues. Without good paying jobs and a strong economy the Sierra Club itself would largely cease to exist. Proponents of using natural gas to make cement are ultimately promoting the movement of jobs overseas and out of the US.
The bottom line is that the Sierra Club and those promoting “Beyond Coal” must ask themselves if they want to take a position that will actually increase CO2 emissions, negatively impact overseas environmental justice communities and export quality jobs, all for the sake of opposing the use of coal in the manufacture of Portland cement.