﻿Lincolnshire hospital shows the way to halving carbon emissions
Is this the first hospital to combine a biomass steam-raising boiler with CHP to halve carbon emissions?
When the energy centre at Pilgrim Hospital at Boston in Lincolnshire was built 40 years ago, heavy fuel oil was the natural fuel to use to generate the steam that would subsequently be used to provide space heating and domestic hot water. Over the years, four steam boilers have served the hospital well — but they were approaching the end of their life.
In this carbon-conscious age and with United Lincolnshire Hospitals Trust (ULHT), which runs this hospital, having signed up to join the NHS carbon-management programme two years ago to reduce carbon emissions by 30% over the next five years, like-for-like replacement was not an option.
Replacing heavy fuel oil with gas would have made a dent on carbon emissions, but the trust was looking for substantially greater reductions in carbon emissions than would have been possible with a simple fuel switch.
The original plan was for a biomass boiler to generate 1.4 t/h steam and a CHP unit with an electrical output of 1000 kW and a heat output of 1070 kW. This plant would have been supported by a dual-fuel packaged boiler producing 6.5 t/h of steam and supported by 630 kg/h from the exhaust of the CHP gas engine.
But there was a major obstacle to this approach. Not enough gas was available, and it would have cost £750 000 to lay a new gas main to bring supplies from the other side of Boston and through the town centre. The cost was considered prohibitive.
That problem led to the trust working closely with Cofely to devise an alternative solution that would not require more gas to be made available.
To make the best use of the natural gas available to the hospital site, a smaller CHP plant has been installed and a much larger steam-raising biomass boiler. The number of steam-raising oil-fired boilers has been reduced from four to two by scrapping three boilers, refurbishing one and installing one new boiler.
The results have been spectacular — a reduction in the hospital’s carbon emissions of 51%, with financial savings of around £210 000 a year and a payback of six to seven years.
The project has attracted the interest and involvement at the highest level of ULHT. Paul Richardson, chairman of the trust, speaking at the formal opening of the new energy centre, said, ‘The message to the trust is that this installation is spectacular — both for the trust and the NHS. The NHS will be looking at this project very carefully.’ He further believes that a 51% reduction emissions has never been achieved before.
Richard Derry, chief operating office of Cofely believes that this is the first time a wood chip boiler has been used in the National Health Service to generate steam. Indeed, many of the measures being introduced at Pilgrim Hospital are being evaluated for use in other trust hospitals. One example is Grantham Hospital, where a reconfiguration of the energy services would reduce CO2 emissions by 2000 t a year.
Financing the project was a challenge in itself, and it was in April 2008, following a tender under PFI rules to include finance, that the trust entered a partnership with Cofely to design, build and operate the new energy centre at Pilgrim Hospital for the next 15 years. Cofely helped secure the funding required for the project, including a £200 000 biomass grant from Lincolnshire County Council and grants from the Carbon Trust and other bodies. Cofely has also assumed the financial risk for the project.
The terms of the contract include Cofely selling steam, electricity and hot water to the hospital.
The contract includes a commitment to achieve an average 5% energy saving each year. Rather than a standard contract format with inflation-linked annual rises, Cofely will achieve any additional revenues solely through the energy savings it achieves. However, inflation-linked rises can only be given if the contractual 5% annual energy-efficiency saving is achieved.
The biomass boiler is rated at 2.9 MW and burns wood chips at around 700°C to produce 3 t/h of steam. The steam serves the main wet heating system and heating coils in the air-handling units. It also supports the CHP unit in the production of domestic hot water. The boiler was made by Binder of Austria, for which the UK agent is the UK representative.
The wood chips are supplied from Thetford Forest and delivered by road to a store with a capacity of 150 t. The daily consumption is about 25 t, representing about five deliveries a week. This is not all extra traffic, however, as the requirement for deliveries of heavy fuel oil is reduced.
Wood chips are drawn from the storage area by hydraulically driven drag-and-flight conveyors to a screw mechanism that transports the fuel to the boiler itself.
Flue gases are discharged up one of the three flues in the 50 m-high site chimney. A cyclone system in the flue removes solid particles to ensure compliance with legislation. The ash residue is about 1% by weight. The initial lighting of the biomass boiler is achieved using 30 sec oil.
The cost saved by displacing heavy fuel oil is estimated at £209 000 a year.
To make the best use of the available gas, a CHP unit has been installed. It is a Jenbacher unit with an electrical output of 526 kW to the hospital supply, at a cost 40% less than mains electricity, and 636 kW of heat. A key benefit of CHP for this project is the carbon emissions associated with generating electricity compared with electricity from the Grid.
Heat from the engine is supplied to a plate heat exchanger at 7.4 l/s and 90°C and delivered to the trust as hot water at 62°C and, during Summer, meets about 75% of the DHW demand.
About 85% of the heat is used at present, and Cofely is looking to increase this figure. One possibility is to preheat steam water, for which a plate heat exchanger is already in place.
This is a high-quality CHP installation with a quality figure of 118; for comparison 105 is regarded as ‘good’.
Contributing to the quality of the installation is the use of Leanox technology by the engine. Most engines are designed for acceleration and use the throttle to enable performance to match required output. However, in normal idle or steady running, this over-capacity reduces efficiency.
In contrast, the lean-burn approach keeps the throttle at almost 100% but changes the air/fuel mix to obtain the required output. Jenbacher has further enhanced this principle using emission sensors to control the fuel, and branded it Leanox.
Annual energy savings from CHP are estimated at 136 000.
The former boiler room is now half empty, with much of the hospital’s energy requirements met by the CHP plant and the biomass boiler. This plant room originally housed four boilers burning heavy fuel oil. Three of them have been removed, one replaced and the remaining one refurbished.
Each of these boilers can deliver 8.6 t/h of steam, and they support the biomass boiler and CHP.
The biomass meets the base load for steam, so the oil-fired boilers are generally only required in the Winter. For security of supply, however, one steam boiler is kept on standby to take over if the biomass boiler and/or CHP unit are suddenly unavailable.
While the engineering concepts are familiar to many people it is their delivery that is the main challenge. This is a working hospital, so there is no ‘window’ to shut down services — even for a short time. To understand the problems, Cofely worked with a liaison team that understands how hospitals work to put forward ideas.
ULHT chairman Paul Richardson indicated the depth of involvement by stressing, ‘The trust and Cofely have complete confidence in each other, and we are confident that the new energy centre will work well.’