Wheat straw provides climate-neutral heating using System 800xA

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_{^{Susanne Nilsson}}_{^{; licensed under Creative Commons}}

From an agricultural by-product to an environmentally friendly form of heat energy – in Emlichheim in the Emsland, you can find Germany’s first combined heat and power station that uses only straw to produce electricity and heat. ABB supplied most of the electrical and automation equipment.

As the first energy producer in Germany, Bioenergiekraftwerk Emsland GmbH & Co. KG (BEKW) is using large quantities of straw as fuel. With a thermal performance of almost 50 MW, the company supplies to industry and households in the region. Specifically founded for this purpose, the power plant has been working since 2006 with the Emsland Group and BE Bioenergie to implement a safe, predictable and environmentally friendly power supply.

To achieve maximum efficiency from the primary input energy when burning the straw, the bioenergy power station in the Emsland makes use of the principle of combined heat and power. Part of the energy is converted to electricity and the other part is used as process heat/heating. A buffer tank containing 4,000 m³ of water compensates demand fluctuations in process steam and heat consumption in order to ensure consistent heat-controlled operation. In this way, BEKW makes use of up to 90% of the primary energy contained in the straw.

Main facts

Industry	Energy & Utilities
Customer	Bioenergiekraftwerk Emsland GmbH & Co. KG (BEKW)
Country	Germany
Solutions	System 800xA
System integrator	Stadler + Schaaf

From the boiler to the heater

Energy production in the combined heat and power straw plant works according to the classic Rankine principle, which describes the generation of steam in a boiler and its expansion in a turbine. In the first step, the bales of straw are transported from the storage area to the boiler house via a fuel bridge on conveyer belts. Shortly before the boiler, the rotating blades cut the twine and break open the bales of straw and convey the loose straw into the furnace, where it burns on a water-cooled vibration grate. The primary and secondary air circulates through 12,000 openings, thus guaranteeing complete burnout of the straw, low emissions and a high degree of efficiency. The released gases are filtered and released into the atmosphere via a chimney stack with an emissions measurement system.

The heat that is generated during combustion is initially used to evaporate the water in the boilers. The downstream superheaters increase the temperature of the steam to 522 °C before the connected generator converts the rotation energy of the turbine to electrical energy. A steam pipe transports the process steam to the Emsland Group; heat is delivered to the connected private households and public amenities.

Wilhelm Pieper, CEO of BEKW

“With the competent support of Stadler + Schaaf, the process-control concepts were implemented with automation, the processes optimized and scheduling changes realized at short notice and expertly.”

Easily control complex processes

For the electrical and automation equipment, BEKW relies on the support of its cooperation partner Stadler + Schaaf, who has access to a wealth of experience in this area, having been an engineering partner of ABB for many years. “With the competent support of Stadler + Schaaf, the process-control concepts were implemented with automation, the processes optimized and scheduling changes realized at short notice and expertly,” says Wilhelm Pieper, CEO of BEKW.

The control system used is System 800xA from ABB. At the core are two AC 800M redundant controllers. The system is scaleable and, through the integration of applications and devices, provides an efficient information structure. For the operating staff, standardized visualization with fast access to all process information is provided from the central station. A fully integrated engineering environment allows a consistent flow of information throughout all engineering phases up to commissioning and over the entire lifecycle of the system. The bioenergy power plant is designed so that it can run for 72 hours without supervision. The control system is one of the first virtualized systems to be installed in Germany, meaning some of the necessary servers for the various services of the control system are virtualized using the software package VMWare. This reduced costs for the deployed hardware.

Peter Schandin, project manager at Stadler + Schaaf

“The main challenges included the unit control system, including the tertiary reserves, taking account of the process steam supply and district heating.”

Communication via optical fibers

Connection to field devices is ensured through 27 S800 remote I/Os. Besides the controller architecture, the entire communication with the remote I/Os via optical fibers is redundant. The three operator stations and the engineering station also communicate via a redundant network structure. They have a total of ten monitors and two large screens. A Profibus connection, which is also redundant, connects the HIMA safety system for burner safety and boiler protection to System 800xA.

The service provided by ABB engineering partner Stadler + Schaaf includes creation of the specifications, detailed engineering as well as the installation and wiring of the entire electronics and automation engineering. Other than the control system, this includes all the instrumentation and the integration of numerous subordinate PLCs via OPC. Stadler + Schaaf also installed the low-voltage and medium-voltage systems. The automation experts from Offenbach an der Queich manufactured and delivered 130 switch cabinets. Following the loop check and commissioning, the first steam was fed into the power plant in July 2013.

“The main challenges included the unit control system, including the tertiary reserves, taking account of the process steam supply and district heating,” explains Peter Schandin, project manager at Stadler + Schaaf. “The coordination and system-neutral integration of the third-party units and black boxes into the process control system were also technically and organizationally challenging,” Schandin continues.

Monitoring other plant sectors

In the medium-voltage range, Stadler + Schaaf set up three ACS800 frequency converters for the forced draft fan, the induced draft fan and the feed water pump. A further 42 ABB ACS850 and ACS350 frequency converters were installed in the low-frequency range. Around 2,700 I&C signals, predominantly from ABB temperature and pressure measurement devices, and a further 650 signals from the electrical fittings of the power plant come together in the control system. Furthermore there are more than 14,000 signals from the PLCs, which are transmitted via OPC. These monitor and coordinate other parts of the power plant, such as screw synchronization, the turbine, the process steam and heat extraction or the flue gas cleaning.