There may be a requirement to replace existing boiler plant because it is obsolete or fireci on high-sulphur coal or another high-emission fuel. lf the cost of new boiler plant is offset against the CHP budget, a stronger case may exist. That is not to say that CHP is only viable in this circumstance. Whilst many companies prefer to remain self-contained, there can be great opportunities where two or more companies on adjacent sites can combine so that the total heat and power loads are better suited to CHP. This may smooth the time-base for the loads and allow larger, more efficient plant than might be the case for a solo scheme. Where there is adjacent housing, hospitals and civic amenities, a district-heating scheme may provide sufficient base load heating, and possibly chilling, loads to justify CHP. As each potential CHP plant is unique, there is no substitute for a site-specific feasibility study, undertaken either in-house or with outside help. That is, whilst !here is a common thread as to where CHP is likely to be of benefit, there is a diversity of fuel prices, reliability of supply, cost of loss of process steam or heat, and the general needs of the potential host company. FEASI BILITY STUDY A CHP feasibility study would generally start with an energy use study, which assesses client requirements and takes full account of the increasingly complex and fluid relationships between power purchase, fuel purchase, power sales and the strategic benefits of distributed generation. Undertaken in-house or by a consultant, the study would determine an outline concept of the size, configuration, cost and benefits of the CHP scheme prior to moving to the second, development phase of the projeci. Alternatively, one or more projeci developers or contract energy supply companies may be invited to assess the requirements, determine a solution based upon their experience and quote a price for contracted supply of power and heat for an agreed projeci term. Here the detailed design and costs are not necessarily declared to the management of the host site, but wrapped into the energy prices quoted. it is vital to thoroughly understand the current and projected energy use on-site in order to determine potential returns from alternative options. The cumulative energy use, size of CHP plant relative to maximum and average demand and whether 'heat matched' or 'power matched' are key items of the feasibility study. MAKALE / ARTICLE Further, the significant change of culture must be fully appreciated. The CHP planı will typically become the main point of supply and will be subject to both planned and unplanned outage. Processes requiring very high security of supply may either gain from the installation of new planı (with suitable redundancy of plan! items) or, where the process is currently connected to a reliable mains supply, the CHP scheme may potentially lose reliability unless adequate redundancy is built in. For instance, three 50% duty machines maybe required, along with supporting safeguards in balance of plant, standby boiler plan! ete., to ensure the required reliability of supply. System efficiency is improved by increasing unit size and the specific capital cost reduces with larger units. However, single large units also reduce flexibility of operation and increase the dependence on a single piece of equipment. Where redundancy of plan! must be built into the calculations, smaller machines may reduce the 'apparent' thermal efficiency benefits of CHP. Typical elements of feasibility study include: O primary products produced by site O examination of electricity and heat demand, profiles and cost, including site shutdowns / holidays O current company thinking on system configurations and permutations to be included in the investigation O plan! schematic and description of steam/hot water use on-site O percentage and temperature of condensate to be returned from process O type of water treatment planı O requirement for waste incinerators, air compressors, refrigeration planı ete., as appropriate O whether !here is somewhere that low-grade surplus heat can be disposed of - river, sea, ete. O determination of age, condition and redundancy in existing planı (including recent equipment which could be retained) O the sensitivity to loss of supply, and consequences if the supply is interrupted O whether special services are to be provided - e.g. carbon dioxide supply for the process, ete. O black-start requirement / island mode capability O single-line diagram of MV/HV systems (and whether changes are required to improve reliability) O site plan, including space available for new planı. From !his follow: O discussions with the management team O determination of a strategy for secure future supply O establishment of the space requirement for new piant O financial modeling, including fuel cost / power sales sensitivity checks O determination of first-cut costs for potential plant solutions ENERJi & KOJENERASYON OÜNYASI 67
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