BURNING RUBBER FROM SHREDDED TIRES AT THE ST. CONSTANT CEMENT PLANT PRELIMINARY RESULTS CIMENTS CANADA LAFARGE LT~E- CANADA CEMENT LAFARGE LTD.

Transcription

1 BURNING RUBBER FROM SHREDDED TIRES AT THE ST. CONSTANT CEMENT PLANT PRELIMINARY RESULTS CIMENTS CANADA LAFARGE LT~E- CANADA CEMENT LAFARGE LTD.

2 BURNING RUBBER FROM SHREDDED TIRES AT THE ST. CONSTANT CEMENT PLANT PRkL I MI NARY RESULTS September 1982

3 I. Cement and the Cement -Maki ng Process "Portland" cement is a manufactured product consisting largely of hydraulic calcium silicates. In Canada, the raw materials are limestone, clay or shale, and smaller proportions of sand and iron cinders. Following the preparation of raw materials by fine grinding, the proportioned raw mix is burned in large rotating kilns, from which it emerges as clinker; this semi-finished material is finely pulverized and treated with approximately 5 per cent gypsum to become the grey powder known as Portland cement. (Diagram overleaf.) The term "Portland" cement is not a brand name; it designates a type of cement and a degree of quality that is fixed by an accepted standard. "Cement" and "concrete" are words often used incorrectly. They do not refer to the same thing. Concrete is a building material consisting of a mixture in which a hardened paste of cement -and water binds inert aggregates into a rocklike mass. The paste hardens through the chemical reaction of cement with water. Concrete, then, is the end product, the material of which office buildings, houses, roads and sidewalks are made. Cement, on the other hand, is the basic ingredient in concrete. In Canada there are five types of Portland cement manufactured: normal, moderate, high early strength, low heat of hydration, and sul phate resi stant. The quality of these cements conforms to specifications issued by the Canadian Standards Association. Some of these cements also meet the requirements of the specifications for oil -well cements established by the American Petroleum Institute. Apart from Portland cements,in Canada there are also Masonry cement and Ciment Fondu.

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5 3. Profile of the St. Constant, Quebec, - / c ' L r - Plant ai The plant, which stands on,850 acres of land near Montreal, started in 1967 as a single kiln operation with a nominal capacity of 450,000 tonnes of cement. An expansion programme, initiated in 1972, culminated in the start-up of a second kiln in February 1975 thus doubling the capacity of the plant. total capital outlay was $68 million. + The Pa ramet e rs Raw Mills Ki 1 ns orsepower 4-2, dimensions 17'6" x 490 feet Capacity (nominal) - 900,000 tonnes per year / Finish mills - 2 of 5*,500 horsepower Clinker storage - 135,000 tonnes / - c- I',._..; Cement storage - 40,900 tonnes Work force Cement is shipped from the plant by rail and truck, to supply the Quebec market, northern New England. and parts of Massachusetts through a terminal in Boston. Other exports are made to the United States by boat from the company's marine termi nal near the old Montreal -East plant... 41

6 4. Kiln Fuels at St. Constant Oil and gas are the fuels used at St. Constant to heat the kilns. in the winter months when gas is not available. Oil is used To generate the high temperatures required in the process, an efficient plant 3750 like St. Constant uses about for each tonne of cement produced. This means that a tonne of product uses 120 cubic metres of gas or 80 litres of oil. In a typical year, the plant produces about 880,000 tonnes of cement using 50 million cubic meters of gas during summer months and 35 million litres of oil duri ng the winter. The cost of fuel has been rising more rapidly than that of other inputs to the manufacturing process. In 1974 it accounted for 24% of production costs: by 1981 it had risen to 30% and is still increasing. Canada Cement Lafarge's response to the rising cost of energy has been to improve the efficiency of its operations by renovating its plants, and in some cases replacing old kilns with new thermally efficient ones. The average fuel consumption per tonne of clinker for all our plants was 5653 MJ in 1975 and 4780 MJ in Improving thermal efficiency can be looked on as substituting capital for energy and the rate at which we can do this depends on the availability of funds. In today's economic climate capital is both scarce and expensive. An alternative route to minimizing the impact of rising energy costs is to replace some of the high cost primary fuels such as oil and gas with supplemental fuels derived from wastes. One of these, which we are currently testing at St. Constant, is rubber fran used tires.

7 5. The Quantity of Discarded Tires is Large A recent Provincial Government study estimated that about 4,500,000 tires are discarded annually in Quebec. This is almost one tire per person per year. Of this number, about 500,000 are recycled; the remainder find their way into dumps or landfill sites. Recycling of Tires Rubber, products 300,000 Blast carpets 100,000 Quay bumpers 50,000 Mi scel 1 aneous 50,000 Total : 500,000 1 J Rubber Should be a Good Supplemental Fuel A typical new car tire contains about 21 lbs. of rubber and 4 lbs. of steel in the form of belting and bead wire. During its life it loses about 5 lbs., so the average discarded tire contains some 16 lbs. of rubber. As far as heat content is concerned, rubber can contain up to 32,500 MJ per tonne which is similar to bituminous coal. The sulphur content is low, 1.2%, compared to oil which may have up to 3%. The St. Constant Pro-iect A number of cement plants in Europe introduce whole tires into kilns at the feed-end where they burn as they move down the kiln towards the burning zone. This approach is not possible in kilns like those at St. Constant, which have chains and other types of heat exchangers in the feed-end. These chains form a barrier to everything but finely ground materials... 61

8 U. We are currently engaged in a series of test burns in which shredded rubber is blown into the burning zone of one of the kilns. Our objectives are: - to find the best way of handling and firing the material; - to find how much of the conventional fuels we can replace with rubber without affecting the process, the quality of our product or the envi ronment. Approximately 400 tonnes of rubber shredded to pieces of 5/8 inch and smaller was stockpiled at the plant. Some of the material was obtained locally and some from Baltimore, Md., because the local sources were unable to provide a suf f i ci ent quantity. The rubber was mainly from steel-belted radial tires and contained some balls of matted belting wire. The steel has no effect on our product but was found to cause problems in the handling system. During test burning, the rubber is transferred from the stockpile to the bin shown in the attached flow sheet by front-end loader. Fran there it is conveyed pneumatically to a second bin on the burner floor. This bin discharges onto a weigh-belt which controls the amount of rubber being fed to the kiln. From the belt it is transferred via a rotary airlock to a pipe through which it is delivered pneumatically to a burner set above the main ki 1 n burner. A preliminary test was conducted in early June, The main focus during this period was on the material handling equipment. Rubber is difficult to handle and tends to form bridges in bins. To overcome this problem air blasters were installed and the sides of the bins lined with teflon to reduce friction. The matted steel, referred to earlier, was found to cause blockages in screw conveyors and rotary airlocks. The problem was eliminated by increasing the size of the air lock on the burner floor and replacing the screw feeder by a weigh-belt. Because of the material handling problems, the maximum substitution achieved was 21%.

9 EZATERIAL HANDLING SYSTEM FOR RUBBER FIRING TEST ON KILN 2 AT ST. CONSTANT - JULY/ f

10 EQUIPMENT LIST ITEM NO. 1 Main Burner Approx. 50'3" Pipe Day Bin Capacity tonnes Cyclone 24" Wide Belt Weighfeeder 18" Rotary Airlock a P1 ant Ai r or Gardner-Denver Compressor Bin Rubber Capacity - 8 tonnes 9" 0 Screw Conveyor 12" fl Rotary Airlock B1 ower Ai r Cannon W

11 9. The equipment was subsequently modified and a second."test was run in mid-july during which period about 100 tonnes of rubber was used. A substitution level of 30% was obtained and samples of the product have been sent to our research laboratory at Belleville to assure its quality. Part of the environmental tests were completed and it was found that no increase in SO2 emissions was observed. The testing of the clinker is not yet complete but preliminary indications are that rubber firing does not alter quality. The Next Steps The initial tests indicate that rubber can be used satisfactorily as supplemental fuel, but further work is required to allow us to define more accurately the optimal conditions for burning rubber and to allow us to design and install practical and efficient permanent rubber handling installation. The Economics of Rubber Firing Have Yet to be Pinned Down The St. Constant plant, if it were to operate at practical capacity, and substitute 20% of its conventional fuel with rubber, would use about 20,000 tonnes of shredded rubber per year. This would be equivalent to displacing 100,000 barrels of oil. To get the required rubber, 2,750,000 tires would have to be shredded and shredding is the bottleneck in the system. The supply of tires, fran the annual discards and the existing stock piles in the province, is more than adequate to meet our requirements but the shredding capacity is not yet in place. It i s not CCL's intention to get involved in the shredding process at this point since we wish to concentrate on developing the handling and firing techno1 ogy. We are at the point of confirming the technical feasibility of using rubber as a supplemental fuel but have yet to derive a clear economic evaluation of the project. The main difficulty is the lack of information on the costs of collection of tires and the capital and operating costs of a shredding plant... lo/

12 10. From our point of view to make rubber firing attractiv"e the price of shredded tires would have to be sufficiently lower than that of oil or gas to provide us with a reasonable return on the development and capital costs of the project. Initial indications are that our investment will be in the order of $900,000. In addition to providing a return on this investment, the price differential would also have to cover the incremental operating costs in terms of manpower, maintenance and electricty. We are confident that we can bring this project to a successful conclusion and establish a permanent rubber firing unit for both of the kilns at St. Constant. The target is to burn upwards of 20,000 tonnes of rubber a year. The result would be a practical and economically sensible way of converting what is currently a waste material into an asset. The Province of Quebec would benefit environmentally frun this disposal of waste tires and also from a number of jobs which would be created by the tire shredding operation. The national economy will benefit frun the conservation of the equivalent of 100,000 barrels of oil. Canada Cement Lafarge is appreciative of the help of Environment Canada which provided a grant of $220,000 in support of this project, through the DRECT program.

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