"There's active work going on in this area, to try and provide the information necessary to the codes organizations as to how they could augment the codes to enable for more innovation in construction materials," she said. This means there's a need for new ideas on how to reduce the industry's emissions, while showing that these new products are safe.
Although the capacity of HBI production in the Middle East and North Africa is increasing, the parallel growth of Electric Arc steelmaking capacity will increase the demand for metallic iron compared to its supply. Therefore, the Middle East may become a scrap metal importer to offset its deficit!.
Although the environmental acceptability of the use of tyres as fuel in kiln systems is dependent on individual plant performance, extensive environmental data has been generated for a variety of kiln configurations and fuel displacement. In general, the different test results have shown that TDF has no adverse effect upon the emissions; that is to say, the use of TDF has not caused a facility to exceed its operating limits (Gray, 1996; Environmental Agency, 1998; Blumethal, 1992a, 1992b). In comparison with coal, particulates, SOx, NOx and HCl emissions generally decline or remain constant with TDF use. Organic emissions, dioxins and furans are also observed to decline while changes in heavy metal concentrations are nominal (Gray, 1996; Scrap Tyre Management Council [STMC], 1992).
Biomass and biomass residues, if sourced in an environmentally and socially sustainable fashion, represent a vast – and largely untapped – renewable energy source. Crop and agro-industrial residues have low bulk and energy density, and for these reasons cannot be transported far from production sites without some form of processing. Residues from large commercial farms and agro-industries can be converted to relatively high-quality and high-energy density fuels for use in the domestic, commercial and industrial sectors through a number of physical, biological and thermo-chemical conversion processes (Seboka et al., 2009). The use of agricultural biomass residues in cement manufacturing is less common in industrialized countries and appears to be concentrated in more rural developing regions such as India, Thailand, and Malaysia. The type of biomass utilized by cement plants is highly variable, and is based on the crops that are locally grown. For example rice husk, corn stover, hazelnut shells, coconut husks, coffee pods, and palm nut shells are among the many varieties of biomass currently being burned in cement kilns (Murray & Price, 2008).
Cement production involves the heating, calcining and sintering of blended and ground raw materials, typically limestone (CaCO3) and other materials containing calcium, silicon oxides, aluminium and iron oxides to form clinker. Clinker production takes place at material temperatures of about 1450 °C in either rotary or shaft kilns. Carbon dioxide is released during the production of clinker. Specifically, CO2 is released as a by-product during calcination, which occurs in the upper, cooler end of the kiln, or a precalciner, at temperatures of 600-900oC, and results in the conversion of carbonates to oxides. Most modern cement kiln systems - have a special combustion chamber called a ‘precalciner’ as part of the preheating tower, as shown in Fig. 1. The limestone (calcium carbonate) decomposition process known as ‘calcination’ (CaCO3 → CaO + CO2) is virtually completed (approximately 95 percent) in the precalciner if 50 – 60 percent of the total fuel required for clinker production is added to this chamber (Taylor, 1990).
In countries like Japan, USA, Denmark, Netherlands, Switzerland and Belgium sewage sludge is used in cement production. In cement production, sludge is usually co-fired with coal in predried form. Predried sludge is easier to store, transport and feed (Werther & Ogada, 1997). The sewage sludge for co-combustion is dried, pulverised and pneumatically fed to the burners. Either the sludge is preblended with coal and fed together, or the two fuels can be fed separately if multi-fuel burners are used. The environmental concerns associated with sewage incineration are significantly reduced when sewage sludge is used as fuel in cement kilns. The organic part is destroyed and the inorganic part, including heavy metals, is trapped and combined in the product (CEMBUREAU, 1997).
It is reported that in kiln systems equipped with high efficient pre-heaters, volatilized recirculation loads of 150 - 200 percent (of the total input) for K2O, 100 – 150 percent for Na2O and 350 - 400 percent for alkali sulphate exist because volatilized alkalis, chlorine and some heavy metal condense on the raw meal grains in the suspension preheater. With the raw meal they return to the kiln where they are volatilized again thereby increasing the recirculation load (Hewlett, 2004; Ghosh, 1991; Taylor, 1990). Some of the alkalis volatilized in the high temperature part of the system (kiln) condense in the cooler parts, causing build-up and blockages in the heat-exchange systems. The sticky deposits attract dust and bind it together to form build-up, which in an extreme case can completely throttle the flow of gas and/or cement solid materials. There are mainly two ways of maintaining the alkalis at a required level, firstly through the careful selection of materials and secondly by bleeding high-alkali dusts from the kiln system (Hewlett, 2004; Taylor, 1990).
Mill scale is a kind of by-product from the steel making and rolling process, its main components are FeO, Fe2O3, Fe3O4 and a small amount of iron and other impurity elements, with the content of TFe around 70%.
Other researchers are focusing on different tactics. Sant, the UCLA engineer, is involved with a research team developing a product they've dubbed "CO2NCRETE." The process relies on "carbon upcycling"—using CO2 emissions captured from industrial activities to produce a cement-like, and potentially carbon-neutral, building material. The CO2NCRETE process is unique, Sant says, because it can utilize the captured carbon emissions as is, without the need for extra processing.
Since sulphur is introduced into the system through the fuel and also with the raw materials, the sulphur content of the fuel can become an important factor in kiln system operation. It is however, important to distinguish between the sulphur in the raw meal that enters the kiln system in the form of sulphates (such as calcium sulphates) and that which enters as sulphides (such as pyrite, marcasite and organic sulphides). The latter can oxidize through an exothermic reaction at 400 – 600oC in sections of the system (for example cyclones) where there is less calcium oxide available. Consequently, the SO2 released is emitted and treated. On the other hand, the calcium sulphates present do not decompose until 900 – 1000oC. This gives the oxides of sulphur an opportunity to react with the alkalis which have been volatilized and also with CaO that has already formed thereby increasing the chance of alkalis and sulphate being removed from the kiln system in the clinker. This is why it is generally possible to use fuels with high sulphur content in the cement industry without significant harmful consequences to the environment (Ghosh, 1991). As already mentioned, if significant amounts of the low melting point mixtures of calcium and alkali sulphates form in and around the preheater sections can lead to blockages.
There is a wide range in the calorific values reported in the literature for agricultural biomass categorically, as well as for individual types. The range in lower heating values -heating value (HHV), alternatively referred to as net and gross calorific value, respectively. The LHVassumes that the latent heat of vaporization of water in the material is not recovered, whereas the HHVincludes the heat of condensation of water. (LHV) of agricultural biomass is from 9.2 – 19.4 GJ/dry ton. The quantity of agricultural biomass residues that are necessary to replace one tonne of coal depends on the fuel’s energy value and water content. As a rule of thumb, a 20 percent substitution rate of agricultural biomass residues for fossil fuel (on a thermal energy basis -) is quite feasible in cement kilns without the need for major capital investment (Seboka et al., 2009; Demirbas 2003 as cited by Murray & Price, 2008).
We can find briquette machine with varies types, screw type (extrude type), hydraulic type, roller type, punching type, etc. These different type briquetters works under different pressures. As a matter of reducing the pressure for briquette making, binder thus plays an important role. Using binder will make some kinds of materials work with different types of briquetter due to the lower pressure requirement. Binder also gives a high strength to the briquette.
Cement plant laboratories check each step in the manufacture of portland cement by frequent chemical and physical tests. The labs also analyze and test the finished product to ensure that it complies with all industry specifications.
In precalciner application where temperature is lower than in kilns, besides the particle size, considerable retention time is required to complete the combustion. In precalciners designed for coal firing where the gas retention time is less than 3 s, often petcoke is introduced directly into the tertiary air where oxygen is highest before mixing with kiln exhaust gases. In some of new precalciner designs the gas retention time is increased significantly to about 7 s by injecting petcoke in a long loop duct before joining the main calciner (Roy, 2002). The combustion of petcoke in a relatively raw meal free hot-zone in the precalciner away from the walls is an important aspect in new precalciner designs and retrofits to achieve high burning rate and avoid build-ups.
LafargeHolcim has developed an advanced range of high early strength cements to help precasters build faster and in a more efficient way. Our cements are an economic solution to improve worksite productivity: thanks to their specific formula, precasters benefit from faster demolding times and increased cycles. Their rapid hardening properties also allow fast concreting, even in cold weather, on major infrastructure projects (airports, roads).
The use of alternative fuels in cement manufacture is also ecologically beneficial, for two reasons: the conservation of non-renewable resources, and the reduction of waste disposal requirements. The use of alternative fuels in European cement kilns saves fossil fuels equivalent to 2.5 million tonnes of coal per year (Cembureau, 1999). The proportion of alternative fuels used in cement kiln systems between 1990 and 1998 in some European countries are as follows in order of importance: France 52.4 percent; Switzerland 25 percent; Great Britain 20 percent; Belgium 18 percent; Germany 15 percent; Czech Republic 9.7 percent, Italy 4.1 percent; Sweden 2 percent; Poland 1.4 percent; Portugal 1.3 percent and Spain 1 percent (Mokrzycki et al., 2003).