Method to produce cement clinker using high sulfur content fuel

Details Method to produce cement clinker using high sulfur content fuel Method to produce cement clinker using high sulfur content fuel

2002-07-13

2003-07-29

Wilson, Gregory (Department: 3749)

Heating

Processes of heating or heater operation

Including passing, treating or conveying gas into or through...

C432S013000, C110S346000, C110S347000, C106S757000, C106S758000

Reexamination Certificate

active

06599123

ABSTRACT:

RELATED APPLICATION (FOREIGN PRIORITY CLAIM)
Benefit is claimed of the prior filing date of Mexican application no. PA/a/2001/007229, filed Jul. 13, 2001 in accordance with 37 CFR §1.55 AND 35 USC §119.
FIELD OF THE INVENTION
This invention relates to a method to produce a cement clinker and, specifically, a method to produce cement clinker using coke with a high-sulfur content as fuel, in order to minimize the problems related to the use of said fuel.
BACKGROUND OF THE INVENTION
The processes and plants used to manufacture cement clinker are well known. Generally, the manufacturing process consists in preparing a raw meal (raw mixture) comprising a mixture of materials such as limestone (CaCO
3
), clay (argillaceous) materials (e.g., SiO
2
, Al
2
O
3
) and iron minerals (e.g., Fe
2
O
3
). Said raw meal preparation includes the steps of drying, pulverizing and supplying said materials in adequate proportions to achieve a clinker with the required composition to obtain a product having the final quality desired. Once the raw meal is prepared, pulverized and homogenized with the required composition, the next steps in the process are: feeding said raw meal to a kiln passing through a pre-heater; calcining said preheated raw meal to transform the CaCO
3
into CaO and C0
2
; feeding the calcined meal to a sintering kiln; sintering (also known as clinkering) the calcined meal to form the clinker compounds such as tricalcium silicate (alite), dicalcium silicate (belite), tricalcium aluminate and tetracalcium aluminoferrite.
Typically, in order to carry out this drying, calcining and sintering process (clinkering), high amounts of energy are required to maintain the high temperatures in the process, the required temperature in the sintering step being about 1450° C., which to achieve and maintain requires the consumption of large amounts of fuel.
Currently, the availability of fuels with a high-sulfur content and their lower cost represent an opportunity for the cement industry, however, their use requires special operation and handling with new methods to facilitate their use without detriment to the continuous operation of the kiln.
One of the available lower cost fuels is petroleum coke having a high-sulfur content. Due to its nature, it typically has a high sulfur content of more than 4.5% elemental sulfur. The sulfur included in the fuel has a significant effect when included in the combustion process. On the one hand, this type of fuel generates the heat necessary to maintain the process temperature. On the other hand, it produces SO
2
which, added to the SO
2
coming from the sulfur content in the raw materials used to form the raw meal, represents a significant amount. This sulfur content can produce blockages in the preheater, if steps or special measures are not taken or adequate compensating methods are not used for processing.
As is known, the SO
2
contained both in the combustion gases as well as in the raw meals come in direct contact with the CaO (lime), forming sulfated calcium compounds (calcium sulfites and sulfates CaSO
3
and CaSO
4
). When subjected to the high temperatures for forming the clinker compounds, which are higher than the decomposition temperature, the sulfated compounds decompose again into SO
2
and CaO. The latter reacts to form new clinker compounds, and the SO
2
carried in the combustion gases returns back towards the kiln solids inlet to again react with incoming fresh CaO. In this way, a continuous cycle is set up with ever increasing sulfur concentrations. Upon reaching high enough concentrations of SO
2
, and having no outlet, sulfur compounds precipitate on the coldest areas of the preheater forming accumulations and blockages, such as in the preheater, the fume chamber, etc. This causes operational disturbances by reducing efficiency and, in more serious cases, stops the operation altogether; for example, when rings form in the clinkering kiln.
In the art, there have been a number of efforts attempting to design installations, equipment and/or processes to enable the use of high sulfur content solid fuels by seeking to solve the problems related to the formation and excessive accumulation of SO
2
. However, the majority of the processes and/or plants to manufacture cement clinker using high sulfur content solid fuel present certain disadvantages with respect to the complexity of the processes and equipment, as well as high costs.
Examples of such prior art are to be found in patents discussed below(which are incorporated herein by reference).
See for instance, the U.S. Pat. No. 4,465,460, entitled “Production of cement clinker” issued to Paul Cosar on Aug. 14, 1984. This relates to the use of high sulfur content solid fuels in the production of cement clinker in rotating kilns. The solid fuel is gasified and the gasified fuel is contacted with a fraction of the raw material used for the production of cement clinker to desulfurize the gasified fuel. The gasified desulfurized fuel is then discharged towards calcining step to provide calories to the same. In addition, it is mentioned that the factors to increase the desulfurization reaction are the gas temperature in the range of approximately 800° C. to 950° C. and the fine granulation of the raw material, preferably to an average the grain size of approximately 100 microns. This patent requires complex facilities and processes to produce cement clinker, which includes additional equipment to reduce the sulfur content or to desulfurize the combustion gases. The combustion gases are placed in contact with a fraction of the raw material to, thus, desulfurize said combustion gases by the partial reaction of the SO
2
with the CaO. However, the control of operation parameters is not mentioned to teach how to avoid the decomposition of the sulfated compounds formed in prior steps, before the calcinated raw material is sintered. In other words, said patent specifically describes a process and installation to reduce to a minimum the sulfated compounds contained in combustion gases specifically. Thus, there is no suggestion as to how effectively to avoid the problems related to the accumulation of sulfated compounds in the overall system.
U.S. Pat. No. 4,662,945 (method) and its divisional U.S. Pat. No. 4,715,811 (apparatus), both entitled “Process and apparatus to manufacture low sulfur cement clinker” issued to Thomas R. Lawall on May 5, 1987 and Dec. 29, 1987, respectively, describe a process and apparatus to manufacture low sulfur cement clinker from cement raw meal containing sulfur or with fuel containing high levels of sulfur or a combination thereof. The apparatus includes a preheater, calcining kiln, clinkering kiln and clinker cooler. A separate source of fuel is added at the end of the clinkering kiln to maintain reducing conditions and temperatures for decomposing the sulfur compounds. The fuel added at the end of the clinkering kiln is carbon or coke fuel with low volatility. This patent relates to the production of a cement clinker with low sulfur content by means of separating the sulfur compounds under reductive conditions. To obtain said clinkers with a low-sulfur content, the use of added equipment and steps specially designed to operate under said reductive conditions are required. The obtained product is a clinker with a low alkaline sulfur content. Notwithstanding, said patent does not make reference either to the sintering temperature reduction nor to the improvement or pretreatment of the raw material effective to avoid the accumulation of sulfated compounds in the system, but focuses instead on eliminating the sulfated compounds during the calcining step.
The U.S. Pat. No. 6,142,771, entitled “Control of cement clinker production using high sulfur fuel in a Lelep-Lepol travelling grate rotary kiln by analysis of sulfur in the end product” issued to Joseph Doumet on Nov. 7, 2000, describes a method and apparatus of producing cement clinker using a high-sulfur content fuel. The high-sulfur content fuel is fed to a burner disposed in the clinkering kiln and mixed with the raw

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