Read part 1 here.
Project example: Myanmar cement plant
Cemcon completed an ECA as an impartial expert on behalf of an internationally active loaning institution for a cement producer in Myanmar. The cement industry in Myanmar is still in the process of privatisation from public ownership (state, governmental bodies and communities). The client, a major industrial conglomerate in the country, operates two almost identical wet kiln lines, each with a 500 tpd rated production capacity. Although both plants were commissioned recently (within the past 3 years) they have a small capacity and are based on wet process kiln technology. The plants were supplied by a contractor on an EPC (turnkey) basis. The technology and equipment quality is below international industrial standards and operational benchmarks are not achieved. In order to retain profitability, and as a direct result of the high thermal and electrical energy demand and coal prices in Myanmar, the plants are subject to upgrading/modernisation to dry process technology and a capacity increase to 2100 tpd.
Wet to dry process
It is obvious that the change from wet to dry process technology will achieve the most significant saving on thermal energy. Compared to an energy consumption of approximately 1620 kcal/kg of OPC cement, a reduction to approximately 762 kcal/kg of OPC cement will be achieved. This is equivalent to 60% of energy conservation. To do so, a 5-stage preheater, a calciner and a tertiary air duct will be installed. The 3.5 m dia. kiln is cut at approximately 86 m and the existing grate cooler is extended but will not reach BAT recuperation figures. For this reason, 762 kcal/kg of OPC cement (cement-to-clinker factor = 1.05) equates to heat consumption of approximately 800 kcal/kg clinker. The calciner is designed with a gas velocity of approximately 14 m/s and a retention time of 5 seconds.
In addition, the following new equipment relevant to energy and CO2 conservation will be installed during the upgrading/modernisation project:
- New two-stage limestone crushing system (300 tph).
- New clay/laterite crushing system (100 tph).
- Replacement of the existing wet ball mill with a modern vertical roller mill (170 tph, 1600 kW).
- Installation of two raw meal silos (23 000 t).
- Installation of a 1.8 MW waste heat recovery system (WHRS).
- Installation of an additional ball mill system for cement grinding (4.2 m dia. x 14 m, 100 tph at 3400 Blaine, 3350 kW).
- Installation of an additional 7000 t cement silo.
- Installation of an additional cement packing station.
Waste heat recovery system
The raw material moisture at both plants is very low. During dry season the raw mix moisture reaches figures below 1%, and in the monsoon season the value increases to 2.9%. However, a low grade (<4500 kcal/kg) lignite coal with a high moisture content of up to 35% during wet season needs to be dried. Due to the low moisture content of the raw materials, the thermal energy content of the preheater exhaust gas is sufficient for drying both the raw mixture and the coal. For this reason the major part of the cooler exhaust air is available for a WHRS, creating 1.8 MW of electrical energy. This energy recuperation/regeneration results not only in a reduction of specific thermal energy consumption of 17.8 kcal/kg clinker, but also provides sufficient energy for continuous operation of the core processing machinery of the plant (the kiln line, in case of electrical power “brown outs” of the public grid).
Because of the design of the calciner, and the multi-channel main burner, the utilisation of alternative fuel and raw materials (AFR) is applicable. There are tremendous amounts of biomass materials (rice husk and sugar cane bagasse) available in the areas surrounding the cement plant.
Sugar cane bagasse is a waste product from sugar milling with a specific calorific value of up to 3000 – 3200 kcal/kg (dependent on process and moisture). Rice husk usually indicates a stable calorific value of 3200 kcal/kg. Only 20% of the available sugar cane bagasse and the rice husk are currently used for energy generation in Myanmar. Hence sufficient material is available to substitute up to 35% of the primary thermal fuel, which at present is lignite coal. This substitution does not result in a further decrease in thermal energy consumption, but provides significant environmental benefits in reducing the CO2 emissions of the plant (Figure 3). Biomass is qualified to reduce the CO2 emissions of the plant by 0.31 t CO2/t of OPC cement, as rice husk and sugar cane bagasse are considered carbon neutral fuel sources. Based on the future capacity of 2100 tpd, the emission savings accumulate to 246 078 tpa of CO2 for each plant.
Not only does the use of biomass AFR result in improved environmental performance, it also results in a significant improvement in financial performance of the production plant through the substitution of the primary fuel coal with AFR, as well as potential emission credits for reduced CO2 emissions.
Change from coal to natural gas
There is a natural gas pipeline available in the direct vicinity of the plant site. Due to the extremely high transportation costs for the low quality lignite coal over a distance of 560 km, natural gas could be an alternative source of primary fuel. However this is dependent on the agreed terms and rate of the natural gas. Utilisation of natural gas, instead of the lignite coal, does not reduce the thermal energy consumption but will lower the CO2 emissions by 0.15 t CO2/t of clinker, and provide an improvement in environmental performance. At a production capacity of 2100 tpd this would result in savings of 97 650 t of CO2 for one plant.
Read part 3 here.
Written by Piet Heersche and Dr Hans Wilhelm Meyer, Cemcon AG, Switzerland. This is an abridged version of the full article, which appeared in the February 2014 issue of World Cement. Subscribers can view the full article by logging in.
Read the article online at: https://www.worldcement.com/asia-pacific-rim/12022014/project_funding_for_energy_conservation_part_2_729/