CPD PROGRAMME
Professional development
The CIBSE Journal CPD Programme
Members of the Chartered Institution of Building Services Engineers (CIBSE) and other professional bodies are required to maintain their professional competence throughout their careers.
Continuing professional development (CPD) means the systematic maintenance, improvement and broadening of your knowledge and skills, and is therefore a long-term commitment to enhancing your competence. CPD is a requirement of both CIBSE and the Register of the Engineering Council (UK).
CIBSE Journal is pleased to offer this module in its CPD programme. The programme is free and can be used by any reader. This module will help you to meet CIBSE’s requirement for CPD. It will equally assist members of other institutions, who should record CPD activities in accordance with their institution’s guidance.
Simply study the module and complete the questionnaire on the final page, following the instructions for its submission. Modules will be available online at
www.cibsejournal.com/cpd while the information they contain remains current.
You can also complete the questionnaire online, and receive your results by return email.
This module explores mid-size biomass boiler solutions and key issues for installations Biomass for commercial building heating systems
There is a clear imperative from the UK government1
for low carbon biomass heat,
and with support under the Renewable Heat Incentive (RHI), biomass boilers have the potential to provide a reduction in carbon dioxide (CO2
) emissions as well as offering
a financial benefit. As with all engineering design, and particularly low carbon or ‘renewable’ technologies, proper consideration is essential to ensure a beneficial – and socially acceptable – solution. The UK has a binding target under the EU Renewable Energy Directive 2009 to source 15%
of its overall energy from renewable sources by 2020. However, it is currently struggling to meet that obligation.2
The UK bioenergy strategy3
suggests that bioenergy has the potential to provide approximately 30% of the 2020 target through biofuels, biorefineries and the recovery of energy from the biomass portion of waste (including anaerobic digestion), so as a way of driving the development of appropriate systems to meet the directive, there is strong support for deployment of biomass heat – primarily driven by the RHI. Not only is there wide variation in biomass
boiler design, but there are also ranges of different biomass fuel types. The vast majority of installations in the UK are ‘woody’ or ‘solid biomass’ – typically wood pellet or wood chip- fed units. This CPD module deals exclusively with ‘mid-size’ automatically fed chip and pellet systems for commercial applications. Equally suited to new build and retrofit
www.cibsejournal.com
schemes, with correct hydraulic design, commercial biomass boilers can be integrated into existing systems, and are best employed as part of a bivalent system (sharing the maximum load with a gas or oil boiler). In comparison to a fossil-fuelled boiler there are, however, significant technical differences in design, operation and maintenance that must be understood and accommodated in order to achieve a successful outcome.
Fuel quality and storage Perhaps the most important factor to consider when appraising a potential biomass installation is sourcing a fuel supply of an appropriately high standard, and provision for its storage on site. Pellet/chip size, moisture content, calorific value and fuel constituents all have a major bearing on boiler operation. The sustainability of fuel supply is central
to the concept of wide scale deployment of biomass heating. The main source of biomass in the UK is timber from forestry, which falls under the remit of the Forestry Act (1967). The Central Point of Expertise on Timber Procurement (
www.cpet.org.uk) gives advice on how public sector buyers and their suppliers can meet the UK government’s timber procurement policy requirements and demonstrate that timber supplied is legal and sustainable. The standards governing the quality of fuel available for wood pellets and wood chips are, respectively, BS EN 14961-2:2011 Solid biofuels.
Fuel specifications and classes. Wood pellets for non-industrial use and BS EN 14961-4:2011 Solid biofuels. Fuel specifications and classes. Wood chips for non-industrial use, specifying limits on size, chemical and physical properties. Ensuring the supplied fuel is in accordance with relevant quality standards is essential in ensuring effective boiler operation. Low moisture content is key to effective combustion. Pellet fuel produced in accordance with quality standards typically has lower than 10% moisture content and, depending on the source and type, wood chip may be closer to 30% (when harvested, timber will have a moisture content typically around 50%, and above 55% moisture content, the fuel is unlikely to burn). Typical calorific values are given in Figure 1. Boiler manufacturers will specify a moisture tolerance range. Excessively high moisture content can lead to incomplete combustion, releasing black smoke and tars that can coat internal heat exchanger surfaces and cause damage to fuel delivery systems. A wide variety of fuel storage options are available, from purpose built rooms to pre- fabricated silos and containerised stores, with automated feed systems typically comprising a mechanical auger or pneumatic arrangement. Physical size, maintenance requirements and access for fuel delivery trucks all require consideration. For these reasons, the installation of biomass plant in dense urban environments can pose logistical challenges. Handling and storage of fuel can also
August 2013 CIBSE Journal 45
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