Less Rejection, Less Waste

Introduction

Rises in the cost of fossil fuels, electricity prices, coupled with stricter legislative mandates by governments around the world, and the increasing effects of global warming have forced cement plants to double their efforts in applying new and efficient technologies to reduce energy consumption. The technology of waste heat boilers and turbines had become fully developed during the 1970s, and throughout that decade and into the 1980s the adoption of waste heat recovery (WHR) plants became very popular in Japan, especially within the cement industry. The high investment cost of these systems at the time precluded their adoption into European cement plants until the 1990s.

A recap

In our May 2011 issue we published ‘Waste Heat Recovery Systems’, by Victor J Turnell, in which the author comprehensively described the advantages and disadvantages of the three main WHR systems currently in use. These are: the Conventional Rankine system, the Organic Rankine system and the Kalina Cycle^®. He reminded us that the preheater exit gases and the clinker cooler vent air are two sources of waste heat that are available and commonly used. In a dry process cement plant about 40% of the total heat input can be rejected as waste heat from the exiting gases of the preheater and clinker cooler. Systems for turning this waste heat into power generation have been and continue to be developed as cement producers realise the urgent need to reduce energy intensity and lower carbon dioxide emissions. Cogeneration systems can either be direct gas turbines that utilise the waste heat, or the installation of a waste heat boiler system that runs a steam turbine system. Energy savings can be substantial. For example, such an energy-saving system can utilise waste heat to generate electricity to cover about 30% of the inhouse power consumption, while reducing CO₂ emissions by up to about 40 000 tpa.

Current projects

One of the latest WHR systems is currently being installed by ABB at Holcim’s Untervaz plant in Switzerland. The system will be based on ORC technology incorporating an exhaust gas heat exchanger and a small thermal power plant using a turbine generator. The WHR power plant is designed with fully automatic remote operations and integrated into the plant’s activities. It is understood that replacement of the existing planetary cooler will increase the power production up to 50%, after which the plant will need 20% less electricity to operate, thus boosting productivity even further. Hepberger has indicated that completion of the project is scheduled for the end of January 2012.

HeidelbergCement began investing in WHPG systems for its three cement plants in China in 2007. For the 5000 tpd Guangzhou plant, it installed a vertical boiler and double pressure turbine, which generates 6 MWe. After 18 months it was achieving an availability factor of more than 95%. The Jingyang plant operates 2 x 6000 tpd kilns, and the company installed a single horizontal boiler and flushing turbine to generate 18 MWe. A similar arrangement was installed at the Fufeng plant, which operates two kilns whose capacities are rated at 5000 and 6000 tpd respectively. Here the electricity generated is 16 MW. Heidelberg has used the knowledge gained from these projects in China for preparation of its project in Turkey and for other projects currently at the design stage.

At the Rohrdorf plant of Südbayerische Portland Zementwerk, Gebr. Wiesböck & Co, a consortium of the Siemens Industry Solutions Division and Kawasaki Plant Systems Ltd (K-plant) is currently installing a new WHRPG system, said to be the first of its kind in Europe. With a capacity of 6.8 MW it will generate 50 000 MWh of electrical energy pa, equivalent to the power consumption for 16 400 households. At the same time, the generation of power from this industrial waste heat will eliminate 31 500 t of CO₂ per annum. The plant is scheduled to start operating in April 2012.

Siemens is supplying the electrical equipment, instrumentation and control, as well as the steam turbine and the generator, and is supervising the construction and commissioning. Kawasaki is providing the overall plant design and engineering for the water/steam cycle, as well as supplying the pressure parts of the boiler, the feed water preheater on the clinker cooler, and the air condenser for the steam turbine.

In March 2011, Holcim Romania announced that it was investing €35 million this year in developing environmental and energy efficiency oriented projects, with the highest investment focusing on a WHR project in the Alesd cement plant. This aims to replace about 15% of the electrical energy consumed in the plant. The €14 million investment is said to be the first of its kind in Eastern Europe. New facilities will also be installed at this plant and at Campulung to increase waste co-processing capacities.

In June of this year, clean energy investor Wasabi Energy signed a licensing agreement with FLSmidth in which the Danish company paid Wasabi an upfront fee to secure exclusive access to the Kalina Cycle^® technology for sale into the worldwide cement and lime manufacturing industries. Wasabi is providing project engineering and commissioning support for an initial four projects. Power generation is expected to begin in the spring of 2012.

Indian potential

Last year, M A M R Muthiah, Vice Chairman of the Cement Manufacturers’ Association (CMA), said that the Indian cement industry could potentially generate 500 – 600 MW of electricity by focusing on WHR through co-generation plants. The equipment required to convert heat into power is calculated to cost about Rs.5.5 – 6 crore per MW, at 2010 prices. The 500 – 600 MW potential is based on about 260 million t of installed capacity of cement, assuming that 40 – 45 million t of fresh capacity is added each year. Birla Corporation’s WHR systems, which were commissioned in stages, at the Satna and Chanderia cement plants now aggregate 22.5 MW, resulting in substantial savings in power costs. It is expected that Birla’s WHR initiative could result in CDM benefits for the company.

In February 2011, FLSmidth won the contract from Vicat Sagar Cements, Gulbarga, to deliver its first WHR system into an Indian cement plant. The 8.4 MW power generating system is based on steam Rankine cycle technology. It will be integrated with the new kiln line (also supplied by FLSmidth) and is predicted to be operational by mid-2012.

Vietnam beckons

Recent figures released by Vietnam’s Ministry of Construction predict that this year total cement production will be 72 million t. As mentioned in previous articles, the country’s flourishing cement industry is resulting in an overcapacity situation where 2 million t are scheduled for export. On average, the consumption level is 100 kWh/t of cement, resulting in a total power consumption estimated at 6.8 billion kWh. Between now and 2020 some 55 new projects will become operational, adding a further 67 million t of cement. This will increase the cumulative designed capacity of all sectors to almost 130 million t, with a total power consumption of about 11.7 billion kWh. This does not take into account the consumption of large volumes of fuel such as oil and coal. The Ministry of Construction has drafted basic norms of technology.

These will require that thermal energy consumption should be less than 730 kcal/kg of clinker, that power consumption should be less than 90 kWh/t of cement, and that dust emission be less than 30 mg/Nm³ for modern plants. In 2000, the Vietnam Cement Industry Corporation (VICEM) had already recognised the importance of WHR. The New Energy Development Organization (NEDO) of Japan granted Vietnam a heat exhaust power system with a capacity of 2950 kWh to be deployed in the 3000 tpd Ha Tien 2 plant. Over the past four years WHR has provided almost 72 million kWh of power for the manufacturing process and has saved 2.1 million t of ADO oil, used to dry the fuel. The system has reduced the heat input and output for the raw mills and the dust filters such that the productivity of the mills has improved by 10 – 15 tph. As a result of the success of this operation at Ha Tien 2, the Vietnam Cement Corporation is now actively implementing similar projects for the Hoang Thach, Bim Son, Binh Phuoc and Tam Diep plants.

In recent months, European suppliers such as FLSmidth and ABB have been demonstrating their expertise in helping the cement industry in Vietnam to embrace the necessary technology to employ WHR plants.

Conclusion

It was the oil crisis in the late 1970s that provided the impetus to create high-efficient energy utilisation in the Japanese cement industry. The idea of recovering large amounts of unused waste heat in plants and converting to electric energy rapidly turned into reality, and very shortly WHR projects accounted for almost 50% of the Japanese market. It took a few more years before WHR systems eventually arrived in Europe, but now the demand for these installations comes from the emerging markets of Asia, e.g., India, China, Vietnam, and from Eastern Europe and Turkey.

This is an abridged version of the full article from Paul Maxwell-Cook, which was published in the September 2011 issue of WORLD CEMENT. To read more download the issue now (subscribers only).

Read the article online at: https://www.worldcement.com/europe-cis/24082011/less_rejection_less_waste_in_the_cement_industry/