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Process
A Vital Unit
For critical project activities like capacity upgradation, there has to be an increment in the capacity of existing coolers.
Aclinker cooler has two equally important objectives. First, it cools the clinker down to 150oC – 200oC to make the clinker acceptable for downstream transport equipment and cement grinding equipment. Second, it is used to recuperate heat as much as possible to save fuel consumption for clinkerisation.
Though there are many types of coolers for cooling the clinker, the state-of-the-art coolers are either grate coolers or cross bar coolers. As cooling is a heat-transmission process, cooling efficiency is greatly dependent on the temperature difference between two media, in this case air and the clinker.
In a cross current cooler, the difference in temperature is pronounced at the start of the process and cooling is thereafter slightly faster and more abrupt (air quenching). Due to this fact, grate coolers, in which the clinker is cooled by air forced up vertically through a thick clinker bed, have become popular in modern large capacity calciner kiln systems. Mechanically as well as operationally, the clinker grate cooler may be considered to be the most complex unit in the clinker burning process.
The clinker cooler has a very strong influence on the heat consumption of the entire pyro installation. Heat consumption in making clinker comprises the following:
-Heat of reaction;
-Heat loss from exhaust gas;
-Surface loss from preheater;
-Surface loss from kiln;
-Cooler loss; and
-Free heat in materials.
Most of the exhaust gas heat is normally used for the drying of the raw materials and fuels and therefore this heat is not wasted. The surface losses of kiln and preheater can probably be reduced to the minimum possible by extensive use of insulating refractory materials in the kiln and preheater. Since the specific heat of air at about 1400oC is a little higher than that of clinker, the cooler loss can be brought down to the surface loss of the cooler, 7 to 10 kCal/kg clinker; the amount of cooling air from the cooler is over 1.0 kg air/kg of clinker (almost the same as required combustion air quantity), if ideal heat exchange conditions are provided. The cooler thus offers a great potential for improving the overall heat economy of a kiln installation. In the course of the rapid development in coolers in recent years, new generations of grate coolers have come into the market. In fact, it has become difficult to keep track of the current cooler generation. However, no great improvements have been made with regard to cooler efficiency and the cooling principle. At the same time, the grate load has typically been increased from approximately 40 to 50 t/d clinker per m2, considering the same clinker temperature, though the widely accepted value is ~45.
Cooler Sizing Vis-a-Vis Operation
Normally, grate coolers are designed considering an operating cooling air flow of 2.2 – 2.4 kg (1.8 – 1.9 Nm3)/kg clinker to achieve clinker temperature of 65oC above ambient at the cooler outlet. However, in many plants, especially at a lower production level than rated, the operating cooling air quantity is found to be on the higher side.
The minimum operating cooling air quantity can be achieved by proper cooler optimisation, which is an art. With proper cooler optimisation during operation stage, the following can be achieved:
-Maximum possible secondary and tertiary air temperatures by using little more than 1 kg air/kg clinker, required for combustion in the recuperation zone where the clinker remains as red. Placement of observation doors on either side wall and on the roof at the right points is found to be very useful during optimisation stage;
-Minimum cooler exhaust air quantity at around 300oC;
-Clinker temperature of 65oC over ambient temperature at the cooler outlet by using total cooling air quantity of ~ 2.2 – 2.4 kg air/kg clinker, or even lower.
Cooler optimisation can be carried out by maintaining:
-Maximum possible clinker residence time in the cooler to achieve the best possible distribution of clinker and cooling air. The clinker retention time in the cooler is determined by the grate surface loading and clinker bed depth;
-Proper cooling air flow distribution;
-Proper tuned PID controller (grate speed vis-a-vis under grate pressure) plays an important role.
Plant Upgradation and Cooler Retrofit
The standard design norms normally followed by most OEMs are given as under:
In India, due to raw material characteristics and cement manufacturers? aggressive attitude, kiln volumetric loading goes for calciner kilns, as high as ~ 7.0. When during the later stage, pyro section upgradation is planned to utilise maximum available capacity of the rotary kiln, cyclone preheater and clinker cooler pose a major problem. Depending on the extent of upgradation modification of existing cyclones, installation of a new preheater or an additional preheater is considered. Again, a new calciner in case of existing SP system and increase in calciner height in case of existing calciner system is considered, if the layout permits. The preheater ID fan is changed to handle higher gas flow and increased pressure drop across the preheater.
Often, the clinker cooler becomes a major bottleneck to support capacity upgradation. Almost all capacity upgradation projects involve increment in the capacity of existing coolers. Even with some extent of compromise with clinker temperature increase at cooler outlet, extra grate area requirement comes out to ~ 50-60 per cent for upgradation, in existing calciner kiln system.
For upgradation of older SP plants, the cooler grate area increment goes to even 150 per cent. Grate area can be increased only if free area is available within the cooler itself or by extending cooler longitudinally or by both methods. In most of the cases the existing layout limits the cooler expansion and thus limits the upgradation scope. It is always advisable to keep a provision in the layout for cooler expansion, by keeping a little longer horizontal length for clinker pan conveyor.
Introduction of new fans or changing cooler fans for higher capacity does not become a major problem.
In most upgradation projects, coolers are retrofitted, mainly aiming at:
-Better cooler efficiency by reducing the amount of heat in the cooler vent air and decreasing the specific fan drive powers;
-Reduced or no clinker fall through; and
-Easy cooler maintenance.
The range of possible conversion measures comprises the following:
-Installation of static inlet grates (specific heat consumption of ~ 15 kCal/kg clinker saving is expected);
-Modification of existing grate plates with new generation plates and improved grate seals;
-Installation of new grate drives and grate bearing assemblies;
-Optimisation and replacement of fans; and
-Improvement of the cooler control system, e.g., by installing clinker bed height sensors as part of the stroke frequency control loop.
Clinker Cooler Exhaust Gas for WHR Boilers
Typically, clinker coolers release large amounts of heated air at 250 to 340?C, which can effectively be used in WHRS system. The steam turbine based waste heat recovery boilers (WHRB) are placed between the cooler and the de-dusting system. Depending on situations/ requirements, various configurations are considered which are shown below. If no modification is made to the cooler and the excess gas is ducted from the cooler exit to the WHRB, then the vent fan should have enough margins to take care of the pressure drop in the heat recovery boiler. If the WHRB is considered later, part of the vent fan size has to be increased accordingly or booster fans have to be provided.
As shown in options 2 and 3, mid taps can be taken from the cooler such that hot gas at 400-450?C is taken to the WHRB, whereas the rest of the cool gas at 100-115?C is sent directly to the ESP. In this case hotter air is available and steam can be generated at higher pressures, improving the efficiency of the waste heat recovery system. Hence up to 15 per cent more power can be generated for cooler systems with mid tap. The mid tap is positioned after the tertiary air take-off point and dampers are controlled in such a way that pressure is balanced within the clinker cooler. However, in these cases, an additional booster fan may be required to pull the gases from the cooler mid-section. Hence this reduces the net power generation from the waste heat recovery system. Part of the hot gases can be utilised for coal drying as shown in options 1 and 2.
(This article has been authored by Jayanta Saha, a Cement Process Consultant based in Navi Mumbai)
Process
Price hikes, drop in input costs help cement industry to post positive margins: Care Ratings
Process
In spite of company’s optimism, demand weakness in cement is seen in the 4% y-o-y drop in sales volume. (Reuters)
Cost cuts and better realizations save? the ?day ?for ?UltraTech Cement, Updated: 27 Jan 2020, Vatsala Kamat from Live Mint
Lower cost of energy and logistics helped Ebitda per tonne rise by about 29% in Q3
Premiumization of acquired brands, synergistic?operations hold promise for future profit growth Topics
UltraTech Cement
India’s largest cement producer UltraTech Cement Ltd turned out a bittersweet show in the December quarter. A sharp drop in fuel costs and higher realizations helped drive profit growth. But the inherent demand weakness was evident in the sales volumes drop during the quarter.
Better realizations during the December quarter, in spite of the 4% year-on-year volume decline, minimized the pain. Net stand-alone revenue fell by 2.6% to ?9,981.8 crore.
But as pointed out earlier, lower costs on most fronts helped profitability. The chart alongside shows the sharp drop in energy costs led by lower petcoke prices, lower fuel consumption and higher use of green power. Logistics costs, too, fell due to lower railway freight charges and synergies from the acquired assets. These savings helped offset the increase in raw material costs.
The upshot: Q3 Ebitda (earnings before interest, tax, depreciation and amortization) of about ?990 per tonne was 29% higher from a year ago. The jump in profit on a per tonne basis was more or less along expected lines, given the increase in realizations. "Besides, the reduction in net debt by about ?2,000 crore is a key positive," said Binod Modi, analyst at Reliance Securities Ltd.
Graphic by Santosh Sharma/Mint
What also impressed analysts is the nimble-footed integration of the recently merged cement assets of Nathdwara and Century, which was a concern on the Street.
Kunal Shah, analyst (institutional equities) at Yes Securities (India) Ltd, said: "The company has proved its ability of asset integration. Century’s cement assets were ramped up to 79% capacity utilization in December, even as they operated Nathdwara generating an Ebitda of ?1,500 per tonne."
Looks like the demand weakness mirrored in weak sales during the quarter was masked by the deft integration and synergies derived from these acquired assets. This drove UltraTech’s stock up by 2.6% to ?4,643 after the Q3 results were declared on Friday.
Brand transition from Century to UltraTech, which is 55% complete, is likely to touch 80% by September 2020. A report by Jefferies India Pvt. Ltd highlights that the Ebitda per tonne for premium brands is about ?5-10 higher per bag than the average (A cement bag weighs 50kg). Of course, with competition increasing in the arena, it remains to be seen how brand premiumization in the cement industry will pan out. UltraTech Cement scores well among peers here.
However, there are road bumps ahead for the cement sector and for UltraTech. Falling gross domestic product growth, fiscal slippages and lower budgetary allocation to infrastructure sector are making industry houses jittery on growth. Although UltraTech’s management is confident that cement demand is looking up, sustainability and pricing power remains a worry for the near term.
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