The Derrinlough briquette factory is a production facility in County Offaly, Ireland, opened in 1957. It ceased production on 26 May 2023. This was five days earlier than its planned closure date of the 1st of June 2023, due to a major mechanical failure. Which itself was months earlier than initially planned.

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The factory was constructed by Bord Na Mona from 1957 to 1959, near Birr in County Offaly. Production started in 1959 and it was officially opened in 1960. Part of the cost was financed by a £500,000 loan from Guinness^[1] in addition to other borrowings.

The original briquette factory in Lullymore was unable to meet market demands by the 1950s as it could only produce about 40000 tonnes per annum even after modifications.^[2] Plans were advanced for two new factories, one located in the Derrygreenagh group of bogs in east Offaly and a second in the Boora group in west Offaly. Construction of Derrinlough started in 1957, with Croghan starting soon after. Derrinlough began production in late 1959 with its official opening in 1960.^[3]

The Derrinlough facility has a design capacity of 135000 tonnes per annum. It is the last peat briquette factory in operation in Ireland (Lullymore closed in 1991, and Croghan in 2000, while the newest factory, in Littleton, closed in 2018).^[4] Production of peat briquettes is due to finish in Derrinlough in 2024 ^[5] but due to poor quality raw material stocks and issues with plant reliability, the closure was brought forward to June 2023.^[6]

Peat is delivered to the factory by rail and road and stored in a large shed for blending and feeding to the factory. The blending allows for a more consistent quality of peat by mixing peats of various densities and moistures, and for a continuous 24/7 supply for the process. A typical blend is approximately 1500 tonnes and has a moisture content of between 50% and 56%, with a density of 220 g/l to 300 g/l. The peat is fed to a large buffer bunker and then passed through a 125kw hammer mill to improve consistency. The speed of the flow from the buffer bunker is controlled to allow the correct amount of peat feed to the factory in real time.

The peat arrives on the 6th floor of the main factory building and passes through screens to remove any fibre or other larger particles of peat. The tailings flow from the screens is fed to the boiler. The screened peat enters the first of 5 18m-long dryers. The peat passes up through each of these dryers in turn, becoming increasingly drier after each pass. The dryers are 3m in diameter and contain about 500 pipes of 70mm diameter. The first 2 dryers contain hot water (at 70-75 degrees Celsius). The last 3 dryers contain de-superheated back pressure steam which varies between 2.3-2.9 bar.

The peat leaves the last dryer at about 10% moisture and is fed to the 5 briquetting presses via pre-packers. Each press has two rams, so the total max output of the plant is 10 runners of briquetted peat. The factory is rated to run on about 18-20 tonnes of production per hour but higher outputs are regularly achieved. The output is determined by the peat moisture and quality. The input/output ratio is approximately 2.5/1. The briquetted peat cools as it is pushed in a continuous line out from the main factory building towards bailing operations. The briquettes are tied into bales of two layers of 10,11 or 12 briquettes per layer. Each bale is 435mm long and weighs about 12.5 kg. From the 10 balers the bales travel to a palletiser and from there on pallets into storage.^[7]

The entire electrical load for the process is generated by a 2.5 mW radial flow steam turbine. The STAL turbine generates at 400 volts 50hz running at 3000rpm. The inlet pressure is 38 bar. The back pressure heats the peat dryers with the remaining steam condensed back and fed back to the boiler drum.

The briquette factory was scheduled to close in 2024, in line with Bord Na Mona's "Brown to Green" strategy. The board has started construction on a 21 turbine 126 mW wind farm^[8] in early 2022.^[9] There are some other proposals for the reuse of the factory site but no plans are at an advanced stage at the time of the plant's final shutdown.^[10]