CPD PROGRAMME Heating circuit flows
Biomass boiler
Buffer vessel
Condensing gas boiler
challenging in terms of space availability, especially in the case of refurbishment schemes. To this end, containerised plant rooms (as
Heating circuit returns
Figure 3: Simplified schematic of a typical bivalent biomass system Tariff
Eligible sizes Tier 1 Small biomass
Medium biomass Large biomass
Less than 200 kWth
200 kWth and above; less than 1,000 kWth
1,000 kWth and above Figure 4: RHI tariff levels for biomass installations (July 2013)
Affected installations covered by these tariffs will receive, each year, a higher Tier 1 tariff for the initial proportion of heat (an energy equivalent of the total installed load output for 1,314 hours per year) and lower Tier 2 payments for the remainder. (So, under current RHI arrangements, there is the potential for unscrupulous or poor design producing oversized installations that would benefit from a larger proportion of Tier 1 payments.) Heat meters, compliant with ‘class 2’ requirements of the Metering Instruments Directive (MID Annex MI-004), must be employed to provide heat delivery data for claims. Ofgem publishes guidance on the requirements for the number and placement of such meters, which depends on the number of heat sources and complexity of the system. In the case of system designs including a back end protection loop, it is essential that this is excluded from any metering, as the heat is not deemed ‘useful’; typically, a meter at the inlet of the buffer vessel will suffice. From the date of a successful application,
the tariff is claimable for a period of 20 years for biomass installations – providing the plant remains in operation – with annual adjustments of tariff levels in line with the Retail Price Index (RPI) Built into the RHI scheme is a ‘degression mechanism’ that will instigate a reduction of the tariff level in the event of a particular technology reaching 150% of the Department of Energy and Climate Change (DECC) predicted expenditure in a budget year. During May 2013, the ‘medium biomass’ category reached its degression trigger point, meaning that new applicants for the scheme since July 2013 face
www.cibsejournal.com
tariff rates 5% lower than those offered on earlier installations.
Maintenance For the operational phase of a project, it is essential to define a robust maintenance regime for biomass boilers. In general terms, to ensure efficient operation, maintain clean flue gas emissions and prevent damage to internal components, the biomass plant will have greater maintenance requirements than a gas boiler. Dependent on the design of the boiler and any ‘self clean’ functionality, it may be necessary to complete weekly tasks such as emptying ash bins or brushing flue ways. Self-cleaning units can reduce this interval and provide a degree of automation to the maintenance regime.
Packaged plant rooms A complete biomass solution includes fuel storage, fuel delivery system, buffer vessel, back- up boilers, hydraulic integration and controls, together with requirements for maintenance access and fuel delivery. Incorporating all of this into an internal plant room can prove
8.6 p/kWh 5.0 p/kWh
1.0 p/kWh Tariff rate Tier 2
2.2 p/kWh 2.1 p/kWh
shown in Figure 5) – including all required system components, flues and external connection points – are becoming available. This approach offers significant benefit in terms of site assembly time and ensures a consistently high quality design and fabrication. Following recommendations in the Egan Report, it is anticipated that offsite prefabrication has the potential to decrease costs by as much as 30%. The application of biomass technology for providing heating for buildings is, of course, not new. However, new systems that include benefits such as more reliable automatic fuel feeds, and improved burner and emission controls, together with a maturing fuel supply market, greater government assistance and increased market competition, are opening up the potential application of biomass boilers. © Jeff House and Tim Dwyer, 2013.
Further reading: CIBSE Knowledge Series 10 : Biomass Heating is a good introductory text, and the freely downloadable Biomass heating: a guide to medium scale wood chip and wood pellet system from the Biomass Energy Centre provides an excellent reference. For practical health and safety provisions, there is an excellent free guide Health and safety in biomass systems: Design and operation guide, published by the Combustion Engineering Association.
References 1 The Future of Heating: A strategic framework for low carbon heat in the UK, DECC, 2012.
2 Renewable energy progress and biofuels sustainability, (ENER/C1/463-2011-Lot2) EC, 2012.
3 UK Bioenergy Strategy, DECC, 2012.
4 Typical calorific values of fuels,
www.biomassenergycentre.
org.uk/portal/page?_pageid=75,20041&_dad=portal &_schema=PORTAL accessed 28 June 2013.
5 The Dangerous Substances and Explosive Atmospheres Regulations, HSE 2002,
www.hse.gov.uk/fireandexplosion/dsear.htm
6 Palmer, D. et al. Biomass heating: a guide to medium scale wood chip and wood pellet systems, Biomass Energy Centre (
www.biomassenergycentre.org.uk), 2011.
7 Palmer, D. et al. Biomass heating: a guide to feasibility studies, Biomass Energy Centre (
www.biomassenergycentre.org.uk), 2011.
Figure 5: Example of a prefabricated, packaged plant room August 2013 CIBSE Journal 47
Back end protection loop
Low loss header
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60