Global Cement recently visited the Khairpur cement plant of DG Khan Cement Company, situated at Chakwal in a rural area in Punjab State, northern Pakistan, between Lahore and Islamabad. Despite the remote location, the cement plant is a model of modernity, demonstrating admirable self-sufficiency in a number of areas and boasting many impressive features.
The mineral-rich Salt Range is certainly not just composed of salt, although it contains three large and famous salt mines of Khewra, Kalabagh and Warcha. Coal is also found in the Salt Range, but what brings cement producers to the region is its high-quality limestone, as well as its strategic position in the developing north of Pakistan and the fact that it is now well-connected with the world-class M2 motorway, which winds it way up steep inclines into the hills around the famous salt-water lake and nature reserve at Kallar Kahar from the vast plain of the Punjab below. Indeed, so rich are the hills in limestone that the twin cement plants of Bestway Cement, and the Dandot Cement Factory near Tobar, are within a long stone’s throw of the DG Khan Cement plant at Khairpur. DG Khan Cement Company is a member of the Nishat group of companies, with businesses including cement, textiles and banking. Global Cement recently visited the Khairpur plant site and was kindly hosted by plant manager Col (r) Hashmat Ali Khan and his colleagues.
DG Khan Cement’s site was established in 2004, and started production in 2007. The plant was officially inaugurated by the then prime minister of Pakistan, Shaukat Aziz. The plant capacity is around 6700t/day of clinker, or 2.21Mt/year, with cement production capacity of 2.43Mt/year.
Cement plant process walk-through
The plant has its own limestone quarry, with a lease area of 6798 acres, as well as an argillaceous clay quarry on site. The present working area of the quarry is 1.35km2, and total reserves of limestone are around 646Mt.
The limestone crusher at Khairpur has a capacity of 1500t/hr, sending material to a limestone storage shed with total capacity of 90,000t. An FLSmidth 52.5 Atox mill, fitted with an RAR-LVT 52.5 air-separator, is used for grinding raw materials at a rate of 500t/hr. Prior to the pyro-system, materials are stored and homogenised in a CF silo with capacity of 25,500t of raw meal. The plant uses a two-pier Rotax-2 kiln with tertiary air-duct and an FLSmidth SF 4 x 7F Cross Bar cooler for clinker cooling. A Brokk 330 remote-controlled demolition robot is used to de-brick the kiln during shutdowns. Clinker is transported by pan conveyor to the mammoth clinker storage silo, with a capacity of 110,000t of clinker. The two OK 36-4 vertical roller mills used for clinker milling are each rated at 175t/hr. The three cement silos at the site have a storage capacity of 21,000t each.
Cement quality control is facilitated with the use of technology such as PGNAA and X-ray analysers (PANalytical CubiX Pro XRD and CubiX XRF). The packing house can bag cement at 600t/hr, using six Ventomatic rotary packers operating at 12,000 50kg bags per hour, while there are also 12 loading positions for trucks. Three bulk loaders are available for delivery of 600t/hr of bulk cement, in parallel.
Waste heat power generation
The DG Khan Cement plant at Khairpur has a total power requirement of 31MW, which cannot always reliably be supplied by the national grid. In order to give the manufacturing facility an uninterrupted supply of power, DG Khan Cement has installed two captive power plants. Firstly, the plant features a Kalina Cycle-based waste heat recovery plant with power production capacity of 8.6MW, manufactured by FLSmidth of Denmark. Wasabi Energy provided FLSmidth with front-end engineering design (FEED), procurement and commissioning services in relation to the Kalina Cycle® technology. The Kalina Cycle1 process uses a binary working fluid of ammonia and water with proprietary and patented processes for varying the ammonia concentration throughout the system and for heat-recuperative stages for increased efficiency. The use of ammonia permits efficient use of waste heat streams allowing boiling to start at lower temperatures. A binary fluid allows the composition of the working fluid to be varied through the use of distillation, providing a richer concentration through the Heat Recovery Vapour Generator (HRVG) and leaner composition in the low-pressure condenser. As the molecular weight of ammonia is close to that of water, a standard back-pressure turbine can be used.
In contrast to the Rankine Cycle, the non-isothermal boiling that results from the use of a binary fluid with variable composition gives a good match with the thermal characteristics of the HRVG so that more of the heat can be extracted from the energy source to enhance the efficiency of the process. Similar considerations apply at the condensing end of the power cycle. By selecting a suitable ratio of the two components that form the working fluid, the boiling point can be adjusted to suit the temperature of the heat source and extract the maximum amount of heat. With this characteristic, of being able to take full advantage of the temperature differential between heat source and heat sink, the process is ideally suited for extraction of useful heat from low-grade sources such as is found at a cement plant. Efficiency improvements of 15-50% are claimed for this type of application.
The waste heat recovery system at Khairpur has a fluid temperature of 340°C and recovers waste heat from the preheater and from the clinker cooler using the patented Kalina Cycle KCS1-2A system specially developed for the cement industry.
Combustion-engine power plant
Secondly, the plant’s other captive power generation unit was provided by Wärtsilä of Finland and consists of two 18-cylinder dual-fuel natural gas and heavy fuel oil Wärtsilä 50DF internal combustion engine electrical power generation units, with a combined maximum power output of 33MW. Each Wärtsilä unit can produce up to 16.64MWe in continuous base-load operation with a heat rate of 7608kJ/kWh, which is equivalent to an overall thermal efficiency of 47.3% at the busbars. The Wärtsilä 50DF lean-burn dual-fuel engine has become popular for power plant installations in a number of countries. It is one of the most powerful gas-burning engines on the market today and has both low emissions and high fuel efficiency which make it a competitive alternative to gas turbines.
According to Wärtsilä, “Important factors in the choice of engine were the need for a reliable, cost-effective electricity supply to the cement-making process, with flexibility in the choice of fuel. Fuel flexibility is an important factor in Pakistan as the year-round supply of natural gas cannot be guaranteed, particularly during high demand in winter months. Furthermore, operating an independent power plant for a cement works is advantageous when starting the large motors commonly used in cement mills with their sudden high starting currents. These requirements are all ideally met by theWärtsilä 50DF.”
“When running on natural gas, the gas fuel is supplied at a low pressure (less than five bar) and the engine operates on the lean-burn Otto process. Gas is admitted into the air inlet channels of the individual cylinders during the intake stroke to give a lean, premixed air-gas mixture in the engine combustion chambers. Reliable ignition is obtained by injecting a small quantity of diesel oil directly into the combustion chambers as pilot fuel, which ignites by compression ignition as in a conventional diesel engine. This ‘micro-pilot’ injection uses less than 1% of the fuel energy required as liquid fuel at nominal load. Electronic control closely regulates the ‘micro-pilot’ injection system and air-gas ratio to keep each cylinder at its correct operating point between the knock and misfiring limits.
In the ‘diesel’ mode, the engines run on liquid fuel oil such as heavy fuel oil as in a conventional diesel engine. The engines are fully capable of switching over from gas to back-up liquid fuel instantly and automatically should the gas supply be interrupted or in the event of any other alarm, while continuing to deliver full power. When the situation returns to normal it is then possible to switch back to gas mode.”
Alternative fuels use
Khairpur is also a leader in Pakistan in the use of alternative fuels for kiln firing, using solid municipal waste and other industrial and agricultural wastes. The plant uses an Eldan Recycling pre-chopper/shredder, screen, wind-sifter and a further Vecoplan shredder, fitted with SSAB Hardox wear-resistant steel hoppers to cope with the abrasive materials being fed into it. The alternative fuels processing facility at the Khairpur plant is large and impressive. The purpose of the project was to replace the use of imported coal with locally-available alternative fuels including agricultural waste such as rice husk, corn cob, wheat straw, bagasse; textile waste; tyre waste; and refuse derived fuel (RDF) from Municipal Solid Waste (MSW). Incoming wastes are stored in separate piles and are first taken to the shredder for size reduction and then transported to the storage bin. The alternative fuels are then extracted using a double screw conveyor and are taken using a Vecobelt pipe conveyor to the calciner floor before being injected into the calciner combustion chamber, controlled through Schenck weigh-feeders.
Bag production at Khairpur
The plant site also has its own bag manufacturing facility, operated by Nishat Paper Products Company Ltd, running three lines with Windmöller & Hölscher equipment, with a production capacity of 800,000 bags/day, for its own use and for the production of bags for other cement producers in the region. The lines are equipped with Flexa 820 flexographic end printers for in-line operation with tubers for multiwall applications, with a print width of up to 157cm. The AM 2185 tuber is used to make three-ply sacks (although up to four plies could be used), while the AD 2390 sack bottomer is also used on the lines. Twin Arcomat 2 robot palletising machines are used to handle the sacks produced. A Paul Maschinenfabrik bag flattening machine is used to pre-condition the bags before use. The plant produces bags not only for DG Khan’s cement plants in Pakistan, but also for its competitors, including Bestway Cement, Falcon Cement, Dewan Cement Ltd, Lucky Cement, Kohat Cement and Maple Leaf Cement. The three lines have a capacity of 190 million bags each year.
Production and social responsibility
The Khairpur plant produces Ordinary Portland Cement and Sulphate Resistant Cement, which are sold locally as well as being exported. The DG Khan Cement Khairpur facility is ISO certified for Quality Management Systems to ISO 9001:2015 and for Environmental Management Systems to ISO 14001:2015.
A free medical centre has been established for plant employees and for local residents, while a water reservoir on site has provided relief for locals from the droughts which are common in the otherwise lovely area. Regular internships and training programmes are made available for students and locals at the cement plant.
Green and pleasant land
Notably, the plant possesses its own plant nursery, orchards, olive trees and rose gardens, including over 30 varieties of roses. It also has 20 acres of agricultural and fruit fields for growing its own produce, which is used in the plant’s canteen, as well as a harvest of around 22t of wheat each year. Products are sold to employees at subsidised rates. Common Myna birds, Acridotheres tristis, enjoy nesting around the top of the preheater tower, no doubt attracted by the warmth of the pyroprocess, but perhaps also by the spectacular views of this tidy and self-sufficient cement plant, situated in an idyllic valley in the heights of the spectacular Salt Range in the Punjab.
2. Validation of the CDM-project: substitution of coal with alternate fuels at DG Khan Cement Company Limited, Khairpur Plant, Report 1577385, TÜV SÜD Industrie Service GmbH
