Mestemacher GmbH

Challenge

The Mestemacher GmbH site is located in the heart of Gütersloh. Surrounded by mixed and residential development, the company has been producing bread and baked goods at the Gütersloh site for 150 years. Pasteurised bread specialities are produced with a naturally long freshness when unopened. The baked specialities are sold sb-packed on the bread shelves of German and international food retailers. Mestemacher is the world market leader in the market niche of long-life wholemeal breads and pumpernickel. The Gütersloh site of the Mestemacher Group produces baked goods and wholemeal breads and has the highest output site in the group. The heating and cooling supply had to be adapted to the increasing production and had to be fundamentally renewed. The individual decentralised heating oil-fired heat generators had reached the end of their life and could no longer keep up with the increased requirements. Due to the surrounding buildings and the lack of space on the factory premises, a solution had to be found to simultaneously meet the requirements of a new central and highly efficient energy supply system without taking up any space relevant to production.    

Solution

In order to reduce energy costs and increase efficiency, a plant that had been unique in the bakery industry until then was built in 2011 and 2012. The new CHP plant was built in a container on the roof of the Mestemacher GmbH factory building at the Gütersloh site. The main unit is a gas-engine cogeneration plant powered by natural gas with a firing thermal output of 2.05 MW. The exhaust gas flow from the gas engine is used to provide thermal power in the form of thermal oil and steam for the Mestemacher GmbH production process by means of a thermal oil heat exchanger and a downstream waste heat steam generator. The engine cooling heat of the gas engine is used at a low temperature level for heating purposes and cold generation by means of a cold absorption machine.

The generated steam is fed to the existing steam collection line and further routed to the heat consumers. When steam consumption is low, the generated steam is stored in a steam accumulator designed for this purpose at a pressure level of 8 bar(a) and then released into the production process at 2 bar(a) during peak load periods. This leads to a continuous utilisation of the gas engine unit. The amount of steam produced is supplemented by steam from the existing and renewed steam generators in such a way that a complete and redundant steam supply is guaranteed at all times.

The thermal oil is heated via a thermal oil heat exchanger and fed to the existing thermal oil furnace system via a newly installed primary circuit. The existing burner in the new secondary circuit takes over the regulation and final temperature setting, which can vary for each baking feed.

The heat absorbed from the engine is transferred to the secondary cooling circuit by means of a plate heat exchanger. The low-temperature waste heat generated here is used both for feedwater preheating and for operating a refrigeration absorption machine and for heating purposes.

The cold absorption machine produces cold for room air conditioning and product cooling. It is supplied with a constant heat flow of 350 kW from the CHP unit.

The electricity produced in the generator in the gas engine at 400 V and with 849 kW is fed directly to Mestemacher's medium-voltage station, from where it is passed on directly to Mestemacher's consumers and to the consumers within the CHP unit. The surplus electricity is fed into the upstream network via the existing transformer.