Choren Industries in Freiberg in Germany reaps the benefits of Totally Integrated Automation in its Beta plant for synthetic biofuels.

Choren Industries had its origins in the Freiberg Fuel Institute, which began performing research on the energetic refinement of organic raw materials and their gasification in the 1970s. After the founding of Umwelt- und Energietechnik Freiberg GmbH in 1990, the company was initially concerned with topics such as drying in steam-fluidized bed processes, power plant optimization studies, and other energy conversion processes. From 1994 on, it has focused its activities on the development of technology for producing synthetic biofuels.

From Alpha and Beta to Sigma

The so-called Alpha plant, a pilot plant for fuel gas and syngas from renewable hydrocarbon sources, was put into operation in 1998. The first liquid products were synthesized from wood on a laboratory scale as early as 2001, and then for the first time in continuous operation in 2003. The successor to this pilot system is the Beta plant, the world's first commercial-scale plant for the synthesis of BtL (biomass-to-liquid) fuel. It is expected to begin operation in spring 2008 and have an annual capacity of 18 million liters of BtL fuel. In addition to the actual process units for the generation of the syngas and the Fischer-Tropsch synthesis, the plant's premises also accommodate all related utilities and auxiliary processes such as biomass handling, storage, and preprocessing as well as systems for process gas conditioning. Choren Industries has now taken another step following the Beta plant and is planning to build the first large industrial plant in Germany, the so-called Sigma 1 plant with an annual production capacity of 200,000 tons (250 million liters).

Choren ensures that the fuel has a consistently high quality by frequent and comprehensive tests

Multistage process

The biomass used in the Beta plant is wood chips that are delivered to the plant and unloaded into underground silos. Impurities such as metal objects and stones are removed, and wet wood is dried using surplus process heat. Then the wood chips are transferred to high silos for intermediate storage.

The heart of Choren Industries is the Carbo-V® process, which is protected by international patents. Using this multistage gasification process, it is possible to convert solid biomass and other feed materials containing carbon into highly pure, tar-free, low-methane syngas that is resynthesized using what is known as Fischer-Tropsch synthesis – a catalytic process for liquefying gas – to form a synthetic biofuel.

During the first stage, the low-temperature gasification process, the biomass is continually carbonized through partial oxidation with air or oxygen at temperatures between 400 and 500 degrees Celsius and broken down into a gas containing tar (volatile parts) and solid carbon (char).

During the second process stage, high-temperature gasification, the gas containing tar is post-oxidized hypostoichiometrically using air and/or oxygen in a combustion chamber operating above the melting point of the fuel's ash to turn it into a hot gasification medium.

During the third process stage, the endothermic entrained bed gasification, the char is ground down into pulverized fuel and is blown into the hot gasification medium. The pulverized fuel and the gasification medium react endothermically in the gasification reactor and are converted into a raw synthesis gas. Once this has been treated in the appropriate manner, it can be used as a combustible gas for generating electricity, steam, and heat or as a syngas for producing BtL fuels.

The Beta plant in Freiberg delivered the first synthetic biofuel in August 2008

A multistage purification and conditioning process then pretreats the gas so that it can be introduced into the synthesis process: quenching, mechanical dedusting, multistage wet scrubbing, carbon monoxide conversion, and purification. In the subsequent Fischer-Tropsch synthesis the reactive components of the syngas, carbon monoxide and hydrogen, interact with a catalyst to form hydrocarbons.

In order to maximize the fuel output, the waxes formed during the synthesis process are further processed using hydrocracking techniques, a standard process that is used in the petrochemical sector to recycle waste substances at refineries, and then separated by distillation into a diesel and a light hydrocarbon (naphtha) fraction.

Gaseous by-products and remaining gas from the synthesis are used in the power station for generating steam and electricity. Additional facilities include an oxygen supply unit and a wastewater treatment plant, and a tank farm with transfer units for transferring the finished products to tank trucks.

Siemens technology in the Beta plant

Good experience with Siemens technology

Siemens gas analyzers had already been operating successfully in the first two CarboCompact and Carbo-V® pilot plants and had proven their worth during the demanding trial runs and experiments conducted in these plants. This positive experience and the excellent technical consulting also favored the decision to use Siemens technology in the first commercial plant for BtL production. “There is always a certain risk in opting for a new supplier. We have been in close cooperation with Siemens for a long time and are familiar with the systems, not only the gas analyzers. We had been using a Simatic S7-400 in the Alpha plant since 1997, also with positive results,” explains Olaf Schulze, technical manager at Choren Industries. “We wanted to exploit this acquired knowledge, so this was also one reason why we used Simatic technology for the gradual expansion of the Beta plant – starting in 2003 with the first expansion stage, the gasification plant, and later also in other process units.”

Choren especially benefits from the broad Siemens portfolio in a complex project such as the Beta plant, as Schulze explains: “We always find a solution with Siemens, both for the process control technology and for the process analytics – even for very specific requirements. The systems are well aligned with each other, thanks to Totally Integrated Automation, so everything fits together. This also applies to the linking of the monitoring and measuring systems with the process control system. Moreover, Siemens technology is well established in the market, so there are many knowledgeable programmers for these systems. In addition, Siemens supports us directly with the programming. And, thanks to the company's wealth of experience in the field of gas analytics, Siemens is able to supply a solution to fit the task exactly. The consulting has a sound basis and is oriented to our requirements and not to selling as many or as expensive devices as possible, as you frequently find elsewhere.”

Comprehensive control for the entire process

Siemens process analyzers are implemented throughout the process. Areas relevant to safety are monitored by the fast, low-maintenance devices of the Ultramat 23 series, while several Ultramat 6 and Calomat 6 devices are used for complex control and monitoring tasks related to the gas production and conditioning processes. Maxum II process gas chromatographs are used in the resynthesis of the syngas into liquid hydrocarbons. All process parameters are transferred to the Simatic PCS 7 system, where they are available to the plant operator.

In addition to the process analyzers and the process control system, Siemens also supplied systems for the low-voltage distribution as well as four transformers. The engineering for the process control system was provided by the Siemens Automation Solution Partner Actemium.

Right on schedule

At the beginning of this year, the plant was fine-tuned so that it will be in operation by spring. Schulze is confident that the first fuel can be delivered as planned in August 2008. So far everything is going almost perfectly according to plan, and Schulze is pleased with the delivered technology: “We are very satisfied with the process control technology and will be using it for our future projects.” This applies particularly to the planned Sigma plant, which will be one of Choren Industries' next challenges. “Although we are only in the scouting phase at the moment, I can see no reason why we should not use Siemens technology again,” Schulze says, adding: “Never change a winning team.”

(All photos: Choren Industries GmbH)

Tank up the sun: SunDiesel®

Synthetic biofuels, also known as BtL (biomass-to-liquid) fuels, are largely carbon dioxide (CO2) neutral and therefore play a major role in protecting environment and climate. Together with Daimler AG and Volkswagen AG, Choren markets one of its range of BtL fuels using the name SunDiesel®. SunDiesel® features a number of positive properties:

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