The Cement Manufacture - Essay Example

Cement: What We Build With Your Full Cement has been a part of almost everything that man has built to improve his life. The chemistry and technology involved in its production has significantly contributed to the development of the world that we have today. On the other hand, environmental and even occupational issues comes hand-in-hand with this industry. Hence, safety measures and standards have been formulated to be able to keep the balance between the benefits and disadvantages that are gained from the cement industry. Cement: What We Build With Cement is a commodity which is derived from processing of limestone and other minerals in high temperature then cooled afterwards and reduced in size until it becomes a fine powder (Environmental Protection Agency [EPA], n.d.). It has become part of man’s lives since the ancient civilizations have used mortars and binders to be able to construct different structures including the great pyramids of Egypt. Through time and innovations, different types of cements have been formulated to be able to meet the demands of engineering (Cement History, 2013). And with these innovations, issues have also risen especially in terms of the generation of wastes and the safety of the people involved in the manufacture of cement. This paper talks about cement and the issues concerning the cement manufacture industry. Environmental and Health Issues in Cement Manufacture The cement industry is a $250 billion dollar worldwide industry and the top six cement manufacturers have taken about 40% of the world market, excluding China. But even with this amount of revenue, the truth that cement is a highly polluting industry and contributes a lot to global warming cannot be denied (The Economist, 2013). Environmental Issues Most of the steps in cement production affect the environment negatively. At the quarrying stage water from this part of the plant may runoff to nearby regions and contaminate water sources with oils and other materials that may be included in the waste water generated (Wansbrough, n.d.). The unreacted raw materials, on the other hand do not pose much harm since they are relatively inert chemicals. Much concern during quarrying is the noise and vibrations caused by explosion and the mining activities if the limestones are taken underground (Van Oss, 2005). There is more environmental concern related to the environmental effects of the clinkering stage since this is where heat, gases and particulates are formed as the raw materials are subjected to very high temperature conditions in the kiln. The burning of limestone particularly poses significant environmental issues (Van Oss, 2005). Particles emitted by the kiln are referred to as cement kiln dust [CKD] which is characterized to be a solid, highly basic or alkaline waste. Not all of the CKD removed by the pollution control devices are recycled back into the manufacturing process. The excess CKD, then becomes a waste which is disposed in landfills or other disposal means above the ground (EPA, 2012). Large amounts of dust in the cement plants are emitted to the environment either through venting or from the machines that carry the cement from one location to another such as conveyor belts or the trucks that carry the rocks. To prevent such environmental effects, it is important that all machineries used in the movement of raw materials and cement is enclosed. Air from these parts and those from the kiln are treated using electric panels charged up to 50 kilovolts and the electrostatic effects of these panels force the dust to the collecting plates (Wansbrough, n.d.). In New Zealand, the dust emission limits from the two main cement manufacturers range from 150 to 250 mg/m3; but in Europe, the limit is even lowered at 50 mg/m3. This kind of requirement is relatively costly but manufactures are mandated to comply to be able to continue their operation (Wansbrough, n.d.). Three main types of gases are emitted as waste in cement plants, namely nitrous oxides (NOx), sulfur oxides (SOx) and carbon dioxide CO2. But among these, CO2 is the main concern because the emission of the other two gases can be minimized by certain on-line process improvement (Van Oss, 2005). Further, emission of CO2 in the cement industry is unavoidable because of the presence of carbon in the raw materials. Apart from the cement production itself, burning of coal to provide high temperatures for the kiln also emits CO2 (Wansbrough, n.d.). Four different strategies have been used by cement industries to reduce the amount of CO2 emitted in the plants. Switching the heat source from coal to natural gas is one of the most common strategies; however this kind of strategy has a disadvantage as well. Fuel availability affects the production of cement if solely natural gas is used; and the cost of the fuel will also put a significant impact on the manufacturing process. Another thing that has to be considered is the efficiency of the kiln in terms of the energy transfers that will occur when shifting from coal to natural gas (Van Oss, 2005). A second approach is an upgrade in the technology of the plant by making the heat zone more fuel-efficient. Process improvement and replacement of better burners may be helpful to establish the cumulative CO2 emission reduction. However, this strategy is very expensive and will be much of a disadvantage to small cement manufacturing plants (Van Oss, 2005). Replacement of raw materials to be able to get CaO is the third strategy used. By using other raw materials, other than lime (CaCO3), there will be less emission of the gas during decarbonation process. Steel slag, with a patent name of CemStar, has been proven to be a good replacement for lime. It is considered to be a good replacement because the steel slag already contains C2S, and even iron, and easily melts; thus requiring a lower temperature to melt and form the clinker. It was estimated that there is a 3 - 10% substitution of lime in the cement manufacturing of Texas Industries Inc. (Van Oss, 2005). The last strategy being considered is the addition of other materials in the cement to lower the amount of clinker being used for the mix. This is however more specific to Portland cement. On the contrary, lowering the amount of clinker in the Portland cement may affect the characteristics; which are specified in the ASTM C-150 standard. Although some countries have been successful in complying with the standards of the ASTM C-150, it is important that cement manufacturers bear in mind that the aim of putting additives is to lower the amount of clinker in the cement, and not to lower the standard specifications for Portland cement (Van Oss, 2005). Health Issues The three gaseous emissions mentioned earlier have negative health effects to humans regularly exposed to these gases. Nitrogen oxide (NOx) can cause respiratory diseases like asthma, and may result in damaging of the lungs. Sulfur dioxide (SO2) affects breathing when exposed to elevated levels and may worsen any current respiratory or heart disease that an exposed person may be suffering from. Carbon monoxide, is also a harmful gas which affects the central nervous system by lowering the amount of oxygen that can be circulated in the organs (EPA, 2013). Employers of cement plants must recognize the health risks that the employees are exposed to. The management must be responsible enough to keep the employees healthy by maintaining health records and providing the necessary personal protective equipment (PPE), and having them replaced when already worn out. Risk assessment and prevention to exposure has also been mandated by some legislative documents (Health and Safety Executive [HSE], 2002). Conclusion Cement manufacture is a long-lasting industry, and similarly, the demands for this commodity will not end. Through the discussion on cement manufacture, it can be clearly seen that there are key raw materials that have to be very abundant to be able to continue with the process. Limestone, silicates and fuel are natural resources, which with time may become depleted with man’s continuous use and exponentially growing demand. Carbon dioxide, as a greenhouse gas, is produced in cement plants. Although lower in emissions compared to power plants that burn fossil fuels (Van Oss, 2005), it is still a contributor to the amount of CO2 in the atmosphere. It is then very important that environment agencies like the EPA, strictly mandate cement plants to comply with standards in terms of the wastes that are being emitted in the production line. Consequently, manufacturers have to recognize that the cement industry must take the initiative to improve their process in the reduction of CO2 emission and be cooperative in minimizing the effects of global warming in the long run. It is undeniable that replacing cement with another material to construct buildings and other structure will be a greater challenge, thus the better way to minimize the negative effects of this industry is a global effort to continue innovating and improving the processes to ensure that the cement industry does not help destroy the environment in the future, while the world is presently building with it. References “Cement History”. (2013). Retrieved from http://www.holcim.com/about-us/company- profile/history/cement-history.html Health and Safety Executive [HSE]. (2002). “Cement”. Retrieved from http://www.hse.gov.uk/pubns/cis26.pdf Environmental Protection Agency [EPA]. (n.d.). “Cement Industry Overview”. Retrieved from http://www.epa.gov/osw/nonhaz/industrial/special/ckd/rtc/chap-2.pdf Environmental Protection Agency [EPA]. (2012, 15 Nov). “Cement Kiln Dust Waste”. Retrieved from http://www.epa.gov/solidwaste/nonhaz/industrial/special/ckd/index.htm Environmental Protection Agency [EPA]. (2013, 12 Sep). “Cement Manufacturing Enforcement Initiative”. Retrieved from http://www.epa.gov/osw/nonhaz/industrial/special/ckd/rtc/chap-2.pdf The Economist. 2013, 22 Jun. “The Global Cement Industry: Ready-mixed Fortunes”. Retrieved from http://www.economist.com/news/business/21579844-worlds-cement-giants-look-set-recoverybut-will-it-be-durable-ready-mixed-fortunes Van Oss, H.G. (2005). “Background Facts and Issues Concerning Cement and Cement Data”. Retrieved from http://pubs.usgs.gov/of/2005/1152/2005-1152.pdf Wansbrough, H. (n.d.). “The Manufacture of Portland Cement”. New Zealand Institute of Cement [NZIC]. Retrieved from http://nzic.org.nz/ChemProcesses/inorganic/9B.pdf Read More