Horst-Heinrich Bieling, BASF, Germany

Rising living standards in many parts of the world mean rising energy consumption and carbon dioxide (CO2) emissions. Having long term secure supplies of energy and raw materials is essential for the success of manufacturers and industries. However, fossil fuel reserves are limited. A leading chemicals company in an energy-intensive industry, BASF recognizes and is addressing the challenges this presents in ensuring a sustainable future.

Power plants are the key to securing competitiveness in energy-intensive production. In the chemicals industry, energy costs account for on average 10-15 per cent of manufacturing costs, and sometimes as much as 50 per cent, as in the case of electrolysis. Combined heat and power (CHP) is a highly efficient technology for the chemicals industry because of its economic and emissions savings. BASF’s CHP plants produce both electricity and steam, raising net fuel utilization to around 90 per cent. They make a major contribution to achieving the company’s goal of reducing specific CO2 emissions per tonne of product sold by 10 per cent by the year 2012 from 2002 levels.

BASF’s CHP plant at its Ludwigshafen site
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CHP has enabled the supply of competitively priced electricity and steam to chemical sites. With investment costs of around €500 ($668) per kW, CHP plants are relatively cheap compared to the separate electricity and steam generation in condensing power stations and steam boilers. In addition, higher efficiencies and optimal automation result in lower operating and personnel costs, which compensate for increasing energy costs.

Maximizing energy efficiency

BASF’s diverse product range totals some 8000 materials, so the company requires huge amounts of energy: in 2005, it used over 25 million MWh of fossil fuels and waste fuels to generate steam and electricity at its major power plants.

Energy is essential for manufacturing chemical products, and securing an optimal supply of energy at competitive prices is a constant challenge for chemicals companies. Rising demand, shrinking reserves and difficulty in accessing resources in some regions have pushed up energy prices. Energy conservation has therefore become a major issue throughout the industry.

The operating mode of the gas turbine CHP plants at the Ludwigshafen production site
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Therefore BASF uses a unique integrated approach (Verbund in German) at its major production sites around the world that links production and energy requirements in an intelligent manner. Each Verbund site integrates its production plants, energy and waste flows, logistics and site infrastructure, so that chemical processes consume less energy, produce higher product yields and conserve resources. As part of the Verbund, the energy integration system optimally utilizes the energy generated as excess heat during exothermic chemical processes in the production plants and converts it to steam. This steam is then fed through pipe systems into the company’s steam network and transported to where the heat is needed.

The efficient use of energy resources is a major priority and because of this the company has been optimizing its energy system. For instance, continued enhancement of the catalyser system in producing acrylic acid has increased the efficiency of the production process noticeably. The amount of energy thus saved is equivalent to the annual energy requirements of about 140 000 single family houses or a large city. About 230 000 tonnes of CO2 emissions is avoided per year. Besides achieving optimal use of energy and raw materials, the logistical advantages of the integrated system save further energies, eliminate emissions and eventually reduce costs.

BASF has six Verbund sites in Europe, North America and Asia; they are located in Ludwigshafen, Germany; Antwerp, Belgium; Freeport, Texas, US; Geismar, Louisiana, US; Kuantan, Malaysia; and Nanjing, China.

Compared to condensing power stations, which produce only electricity, CHP plants achieve much higher fuel efficiency by simultaneously generating electricity and steam. Since the demand for steam in the chemicals industry is high, cogeneration offers ideal conditions for the efficient use of energy. In contrast to district heating networks for heating buildings, cogeneration plants in the chemical industry can be operated to almost full capacity all year round. BASF’s concept for energy supply is therefore based on CHP plants that combine gas and steam turbines. The major advantage of this combination is that it allows close to 3.5 times the amount of electricity to be generated from the same amount of process steam, compared to a cogeneration plant with conventional boiler and counter-pressure steam turbine.

BASF currently operates 16 CHP plants worldwide, which have a combined capacity of 1800 MW. These plants generate the required amount of steam and a large amount of electricity at almost all of the company’s large production sites. Major facilities are found at the six Verbund sites. In addition to the power plants owned and operated by the company, seven further steam-coupled gas turbine plants are operated by partner companies at BASF sites and serve mainly to fulfil the requirements at these sites.

State-of-the-art gas turbines

BASF operates two CHP plants at its Ludwigshafen site. The latest CHP plant has been in operation since May 2005. The plant generates 450 MW electricity and 630 tonnes of process steam per hour. The fuel used is converted with a total efficiency of around 90 per cent and CO2 emissions are reduced by more than 500 000 tonnes per year. BASF has invested €240 million in this plant. This investment has greatly decreased the proportion of electricity purchased from external suppliers and has made the company more energy independent.

BASF’s Ninjing site fully integrates the energy and chemicals production processes
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The centrepiece of the Ludwigshafen plant comprises two natural gas fired gas turbines. Compressors in the turbines pressurize the inlet air to 17 bar. Each turbine has 24 burners, which burn up to 50 000 m3 of natural gas per hour.

State-of-the-art gas turbines can be operated at temperatures up to 1350 ºC. The heat places enormous stress on the materials and is controlled by highly temperature-resistant materials and a sophisticated air inlet cooling system. In the first two rows of the four-stage turbines, the blades are therefore made partly from directionally solidified special steel and partly from a metal with a specially developed single-crystal structure. The blades are also provided with a protective outer coating, while on the inside they are cooled with air that enters through tiny channels to ensure the material temperature inside remains below 800 ºC.

Energy from the rotary movement of the gas turbines is transmitted to a generator, which produces electricity. The combustion gases from the gas turbines are cooled to 550 ºC and are used in downstream waste heat boilers to produce up to 630 tonnes of steam per hour. The recovered steam passes through a steam turbine, which generates additional electricity before the steam is released as thermal energy into the pipe networks. Each of the two gas turbines has an electric power output of around 185 MW; the steam turbine has an output of 80 MW.

CHP sites worldwide

A CHP plant has also been in operation since 2004 at the Verbund site in Nanjing, China – a 50-50 joint venture between BASF and Sinopec, a large Chinese petroleum and chemicals corporation. Modelled on BASF’s headquarters in Ludwigshafen, the plants in Nanjing are linked together. The CHP plant functions in the same way as its ‘big brother’ in Ludwigshafen.

The company’s Antwerp site is also supplied by its own gas and steam turbine power plant. It provides the site with 400 MW of electricity and 300 tonnes of process steam per hour.

Spain is one of the BASF Group’s most important centres in Europe – both as a production and marketing site. Since 2003, the electricity, gas and steam requirements of the site have been supplied by a power plant operated by Tarragona Power, a joint venture between RWE Energie and Iberdrola. The gas and steam turbine power plant is located on the BASF site and has an output of 400 MW. The sum invested was more than €200 million.

The BASF Group’s energy balance for 2005 makes impressive reading: of the 25.7 million MWh of fossil fuels and residual waste used, 6.3 million MWh of electrical power was generated, primarily by means of cogeneration technology, compared to 4 million MWh in 2004. This represented around 47 per cent of the BASF Group’s total electricity consumption of 13.5 million MWh in 2005. The remainder of the required electricity was purchased from the public networks. In 2005, a total of 53.3 million metric tonnes of process steam was provided via steam networks within the BASF Group, and 55 million tonnes was provided in 2004. At the group’s plants worldwide, 46 per cent of this amount was generated by using excess heat from chemical reactions and by thermal recycling of waste.

Why CHP makes sense

A guaranteed energy supply is vital for the survival of any chemicals company. This applies especially to plants that require a start-up phase of several days before they begin producing to specification. Therefore it is essential to use tried and tested components that have already proven their worth in continuous commercial operation. Expertise, especially in constructing new plants and when operating and repairing existing power plants, is extremely important.

Besides their economic advantages, CHP plants have a lesser impact on the environment and help to conserve valuable resources. Optimal utilization of primary energy sources significantly reduce CO2, sulphur dioxide and dust emissions.

With its CHP plants, BASF has created the basis for energy utilization that is ideally suited to its needs. The company has an optimized ratio of electricity and steam generation, where steam generation has been maximized due to cogeneration. The Verbund principle ensures the optimal supply of production sites with steam and electricity, including usable waste heat of the procedural production. BASF is thus an example of how site conditions and suitable technologies can be attuned well to each other. The efficient use of fuels results in cost advantages and low emissions.

Innovations, efficiency and economic viability are ultimately the central issues for the chemicals and all other industries, and CHP plants clearly fit the bill.

This article was first published – entitled “Chemical reaction – an energy-intensive industry finds the solution in CHP”) – in Cogeneration & On-Site Power Production, March-April 2007. The article is available online at www.cospp.com