News 2008

Munich, April 28, 2008

BTL production plants need nitrogen for neutralization

Choren Industries GmbH
Choren Industries GmbH

In the Saxon town Freiberg, the company Choren Industries GmbH is building a modern plant for the production of a synthetic automotive fuel obtained from biomass. The production should commence in 2008.
In accordance with the applicable accident prevention regulations, gaseous nitrogen has to be used during repair works and inspections in BTL production plants for rinsing the plants in order to prevent dangerous plant conditions occurring.
BAUER KOMPRESSOREN, the specialist in the high pressure gas sector, provides an efficient compressor station for this purpose with a generous storage capacity, where the gas coming from a supply unit is compressed to 200 bar for storing purposes.

The worldwide fossil oil reserves will not be at our disposal forever, but will already be depleted in the near future or it will require considerable expense to extract them from the oil fields. Therefore, the German government has taken measures to restrict oil imports and to reduce C02 emission in the future. For this reason and due to the growing energy demands worldwide, the relevant industries are already making it a priority to find suitable alternatives to crude oil. Here, Choren offers a reasonable solution: to obtain synthetic automotive fuels from renewable energy.

Choren Industries GmbH sets standards

Based on the knowledge gained by the relevant industries in Germany during the nineteen-twenties concerned with the production of synthetic automotive fuels, Choren Industries GmbH, with the collaboration of appropriate partners (e.g. Daimler AG, Volkswagen AG, SHELL), is trying to design and build tailor-made BTL production plants to this end reflecting the latest technical expertise.

One of these plants, which - on schedule - will take up production in the year 2008, is presently being built at the location Freiberg. In the production plant, about 80 employees will work 3 shifts round the clock. The factory will produce about 18 million liters of BTL fuel. This volume is the equivalent of the yearly requirement of about 15,000 passenger cars. The installation of further large plants at different locations in Germany is being planned.

By the year 2020, it will be possible to save 3 million tons of CO₂ with 10 to 15 such Choren BTL plants. This planned potential could contribute considerably to realizing the climate protection targets set by the German government.
Besides reducing pollutants and oil imports, the rising price of crude oil may be the decisive factor to investment in this sector. This upward trend will slowly level off at the level of production costs for synthetic diesel fuel. The forecast for the next 30 years is: the market share of BTL fuels will be around 20 %.

What is BTL diesel?

Petrol or diesel fuels obtained from different primary energy carriers using what is known as the Fischer-Tropsch synthesis are designated as synthetic automotive fuels. During the BTL production, the energy carrier used is not natural gas or carbon, but biomass obtained from renewable sources, such as waste wood from forests, horticultural waste from public parks, organic waste substances, straw, etc.

In the first stage, the primary energy carrier is converted to a synthesized gas which then will be synthesized to fuel with the aid of a catalyst.

Thus, if the raw material is biomass, BTL fuel will be obtained (biomass-to-liquids, also called SunDiesel ®).

Advantages of BTL diesel

Some of the advantages of BTL diesel are:

  • The liquid fuel generated via the FT-synthesis can be used without any adjustment to existing infrastructure for diesel fuels.
  • The automotive fuel is extremely clean; it does not contain sulfur or aromatics.
  • It suits all diesel engines (hence, no modification of the engine systems required).
  • Compared to fossil fuels, it produces 30 to 50 % less exhaust emissions; it is largely CO₂- neutral, has a high energy density and is biodegradable.
  • A convincing argument for BTL diesel is its high cetane number of over 70 (measure of the ignition performance; the EU minimum measure is 49 approx.).

Why use nitrogen as inert gas?

As is generally known, because of its fixed triple bond, nitrogen is an extremely inactive gas at low temperatures and is not combustible. In case of shut-down (inspections) or emergency cutout, this chemical property of the gas serves during the BTL process for rinsing and rendering inert the high pressure synthesis processes. In the process, the nitrogen in the storage system is rapidly expanded into the plant components and the circulating hydrocarbon-containing gases will be forced out of the reactors. These gases are evacuated and safely thermally disposed of via a combustion chamber. Afterwards, the high pressure gas compressor will feed gas from the low pressure gas network of the Beta plant in order to replenish the nitrogen gas used during this process at the preset pressure level.

Gas recompression

Concrete building with H.P. compressor system model GIB 15.3-11-5
Concrete building with H.P. compressor system model GIB 15.3-11-5

The pressure increase from 9 bar to 200 bar is realized by a gas compressor unit of type GIB 15.3 -11-5, which in industrial use has proven itself to be the best. It is aircooled and lubricated by a high pressure oil pump. The compressor block compresses in 2 stages with respectively 2 double stages. The normal delivery capacity is about 45 m³/h, in relation to an initial pressure of 9 bar. The generated condensate, which consists of a water-in-oil emulsion, is collected in a condensate collecting tank.

On the aspiration side, the gas compressor is mechanically linked with the low pressure network of the nitrogen supply station of the Beta plant. The gas is fed in with 9 bar. In the compressor intake line, pressure and gas temperature of the medium are monitored. An integrated buffer tank dampens the pulsations coming from the piston of the 1. stage. The temperature-controlled flow heater with 2 kW heating output heats the medium to the predefined intake temperature. On the pressure side of the compressor, a gas scrubbing stage P61 is installed for removal of oil aerosols and for secondary gas drying. It consists of a filter package with activated carbon and molecular sieve.

The plant is operated semi-automatically. That means that it is started manually and shut down automatically via a final pressure sensor when it reaches the final pressure. It is controlled and monitored by the BAUER B-CONTROL which has proven itself ideally suited. It is a freely programmable electronic compressor control with a modern display.

It monitors all pressures and temperature of the plant, as well as the motor overcurrent. If the preset values are exceeded, the plant cuts off automatically and signals the malfunction to a local service station by means of a general malfunction message.

The weatherproof housing

The fully plumbed and compact compressor unit as well as the electric controlling and monitoring switch box are integrated in a weatherproof walk-in concrete building which is provided with all necessary ventilation and exhaust equipment together with a heating system for winter operation. The heating elements (2 kW capacity) are switched on when the room temperature falls under +5 °C.

From the noise point of view, the building has been planned in such a way that there is no noise pollution for the environment. The sound pressure level is under the value of 69 dB (A), measured at the distance of 1 m according to DIN 45635.

The H.P. storage reservoir

The H.P. storage reservoir
The H.P. storage reservoir

Storage tanks made of a high-strength material are used. They are designed and manufactured in accordance with to the European pressure vessels directives. The vessels are TÜV-approved (German Technical Inspection Authority).
The individual pressure vessels are combined to form a stowable storage assembly. In order to maximize the amount of rinsing gas available at short notice for unforeseen works at the BTL plant, 5 such storage assemblies have been plumbed together to form a common single-bank storage system.
The useable volume for rinsing depends on the pressure levels existing in the plants.


Choren sets targeted standards for expanding future BTL production and therefore, it is hoped and it is also very important that, with regard to the specific advantages of BTL diesel, such plants will be promoted not only in Europe, but also worldwide, in order to protect subsequent generations from an environmental collapse.
With this plant, BAUER KOMPRESSOREN has already contributed to protecting the environment and will continue to try to proceed on this path in new projects.

L. Kühlwein, graduate engineer, project engineer in the industrial sector

Drygalski-Allee 37
81477 Munich, Germany
Tel.: +49 (0) 89 78049-0
Fax: +49 (0) 89 78049-167
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