Chiller Hire Keeps Digester on Stream

A packaged chiller solution supplied by Andrews (UK) Chiller Hire enabled a waste processing plant to maintain full operational status of its anaerobic digesters by reducing elevated waste temperature by at least 10oC, creating an ideal for environment for bacteria to produce usable gas output. The company needed to reduce the temperature of waste to no more than 40°C, with approximately 90,000 litres of waste processed on a typical day.

The Process

Anaerobic digestion is the natural breakdown of organic materials into methane and carbon dioxide gas and fertiliser, the reaction is either naturally occurring or takes place within an anaerobic digester; an industrial process for handling large quantities of waste and a preferred environmentally friendly method.

There are essentially three main options for dealing with organic wastes:

    bury it – a landfill options which is unpopular

    burn it - which means incineration, gasification or pyrolysis

    bio-digest it - which means either anaerobic digestion or composting

The process of anaerobic digestion provides a source of renewable energy, since food and other ‘green’ waste is broken down to produce biogas (a mixture of methane and carbon dioxide), which is suitable for energy production.  The biogas can be used to generate electricity and heat to power on-site equipment and the excess electricity can be exported to the National Grid.  Also, after removing the carbon dioxide (and other trace gases using a variety of methods in a process known as upgrading) the remaining methane is known as Renewable Natural Gas or Biomethane.  The uses for biomethane are therefore as varied as are those for natural gas, for heating, cooling, as a source of chemicals, fertiliser or hydrogen.

The Problem

When this major waste processing organisation experienced a slow-down in output due to an unexpected rise in waste processing temperature to 50oC, caused by equipment malfunction, it became too hot for the bacteria to produce gas.  A call went out to Andrews Chiller Hire.

With more than 25 depots nationwide and access to experienced engineers 24hrs, seven days a week, Andrews Chiller Hire is able to respond promptly when an emergency situations occurs.

The swift reaction and local presence meant that Andrews Chiller Hire was able to conduct a thorough site survey within 24 hours of receiving the initial call from the waste processing plant. It allowed a regional technician and the customer to liaise directly and make a swift decision about which size chiller would best suit their needs.

A stand-alone solution was required until their equipment could be repaired or replaced and put back on stream.  To return the plant to normal processing duties Andrews delivered a total integrated solution including a 375kW chiller along with a generator and fuel tank to help bring temperatures down to the desired level.  Once installed, the chiller reduced the temperature of the waste processing by 10oC, allowing proper bacteria reactions to take place and biogas manufacture.

Anaerobic digestion is the only system for dealing with organic waste which is sustainable, recovers the maximum energy, is a completely closed system with no emissions to air or land, which retains the fertiliser and water content, and facilitates the recovery of heavy metals

The intervention of Andrews Chiller Hire meant that the environmental waste company was then able to begin reproducing gas, feeding a turbine to re-start electricity production from the digestion plant.