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HomeMy WebLinkAboutKotzebue Wind to Heat Project Thermal Source Alternative Analysis - Apr 2019 - REF Grant 7014015TechnicalMemorandum 6 Draft Version.2 City of Kotzebue Water Treatment Plant THERMAL SOURCE ALTERNATIVE ANALYSIS April 2019 EXISTING CONDITIONS The Kotzebue Water Treatment Plan (WTP) being designed will provide high level water treatment for the citizens of Kotzebue. Current demand for potable water averages approximately 200 gallons per minute (gpm). The new WTP is being designed for a flow rate of 300 gpm, with the ability to expand to 450 gpm. Based on current design development, the WTP will be housed in a building approximately 70’ by 180’. The building heating requirements will be provided by a glycol/water loop sending heated liquid to air handlers, fan coils, unit heaters and cabinet fans. Hot water/glycol will be sent to each unit and the heat transferred to the building via a coil. In addition, the distributed water will seasonally require heating to assure proper circulation. This is based on maintaining an outgoing temperature of 42oF in the water loops and includes heating raw water as well as any heat loss in the distribution loops. This heat will be transferred to the water prior to exiting the WTP for distribution or a portion added by Kotzebue Electric Association (KEA), as is current practice. The base option for providing the thermal requirements for the WTP is for the building heating being supplied by an oil-fired boiler with the distribution heating being provided from the Kotzebue Electric Association, Inc. This is the arrangement for providing thermal heating to the existing WTP. The purpose of this report is to explore options that should be considered by Kotzebue for the WTP thermal needs that may be less costly, more environmentally sustainable, provide additional beneficial impacts or better accomplish overall operations. These options are: Oil-fired boiler – This option would include all thermal requirements being supplied by oil fired boiler(s) located in the WTP. Design requirements would include 100% redundancy. Dual fuel boiler – This option would include all thermal requirements being supplied by a biomass/oil fired boiler located on land near the WTP with heat transfer equipment installed in the WTP to provide all building heating, raw water heating and loop water heating. Central Heating Plant (waste heat from KEA) – This option would involve KEA supplying all thermal needs of the WTP from recovered heat off their engine driven generators. A sub-option would be for KEA to supply only the raw water and loop water heating. Solar (thermal sourced from existing PV / solar heating at the WTP). A December 2012 study identified significant quantities of excess biomass was being generated in Kotzebue in part due to the incoming shipments utilizing cardboard and wooden pallets. One option identified for the utilization of these biomass sources was to provide all, or a portion, of the thermal requirements for the WTP. The current WTP relies on an oil-fired boiler to provide the thermal requirements of the building and operation, while the heating of water for the distribution loops is provided from recovered thermal energy from KEA. The thermal energy supplied by KEA is recovered from their oil-fired generators. The return line of the Lagoon loop is directed to the KEA electrical generation plant where plate and frame heat 53 Technical Memorandum 2 exchangers are used to add heat to the potable circulated water. The heated water is sent to the WTP via the return line. Heat is added at the direction of the WTP operators. It is approximately 2/3 of a mile from the KEA plant to the WTP. FUTURE OPTIONS Based on the preliminary design and review of operating conditions, Tetra Tech has developed an estimate of future thermal needs of the WTP. The calculations indicate that, at WTP design flow rate, the system will require up to 1,950,000 BTUs/hr to provide building heating, raw water and returning loop water heating. This number includes 700,000 BTUs/hr for restoring heat lost in the distribution loops. This is based on historical data from 2016 to 2018 of the heat supplied by KEA. All calculations used for comparison were based on historical average climate conditions and will need to be adjusted to expected temperatures. The systems would provide less than design temperatures during extreme conditions. In addition, the final system will require greater volumes of fuel once the efficiency of thermal transfer from the boiler to the building heat and water loop heating is calculated. This increase could be approximately 20%. Attachment 1 shows the assumptions and calculations used in this comparison. The heat load calculations show that a 60 HP boiler could supply all the thermal requirements of the water system, including building, loop water and raw water heating. At the maximum future flow of 450 GPM, this would increase to 75 HP. For this analysis, the base load will be based on 75 HP of boiler capacity with each option designed for 100 % redundancy. Heating Loads Preliminary heating loads required for the new WTP have some components that are relatively easy to estimate and others that include some uncertainty. The three major heating functions are: Building Space Heating: To heat the existing WTP, the City used 14,600 gal of fuel oil in FY 2017 and 15,900 gal in FY2018. Although the new WTP is proposed to have a significantly larger footprint, it will be insulated to higher level and provided with heat recovery ventilating units. The preliminary estimate for heating the new WTP in an average year is just over 1,000 million BTUs per year which equates to about 10,000 gal of fuel oil, Water Heating within the Process Area: The operators report an increase of several degrees in water temperature from the raw water supply to the treated water discharge. This may be provided by pumping energy imparted to the water or building heat being transferred to the water. The new WTP will pump the water to higher pressures required by the membrane processes. An increase of 1 to 3 deg F is not unusual in other membrane plants. How much of this increase is due to pumping and how is due to heat transfer from the building spaces is not precisely known. For this analysis it is assumed that any increase comes from scavenged building heat. This thermal transfer is included in the boiler sizing. Add-Heat to the Distribution System: Presently, the amount of heat added by KEA to the water circulation system varied from 3,582 million BTUs in FY17 to 568 million BTUs in FY18. Based on the agreed upon adjustment factor of 70% of the cost fuel oil heating, the cost of adding heat to the distribution has varied from over $90,000 in FY 17 to about $17,000 in FY18. Tetra Tech has calculated the required addition of water loop heating, based on a loop temperature of 42oF. 54 Technical Memorandum 3 Option1 - Oil fired boilers at the WTP Under Option 1, the boiler system will be designed to provide all thermal requirements of the building heating and water circulation loops. For purpose of this study, it is assumed that the oil-fired boiler at the WTP would provide all the thermal needs of the water system. Required capital expenditure would include two (2) 75 HP oil-fired boilers installed in the WTP building, a primary boiler and a redundant boiler at 100% of design capacity. Glycol loops would be installed to provide the building heat with a separate loop designed to transfer heat to both the fresh water and to the loop return lines. Based on the above assumptions, the heating of the building and water loops at design flow rate would require approximately 98,900 gallons of oil annually at a cost of $456,900 based on oil cost of $4.62 per gallon. Option 2 – Dual fuel boiler This option is to allow the use of biomass from shipping activities to provide the thermal requirements of the water system. The system would be housed in a building separate from the WTP and the building would include biomass receiving, processing and storage. The biomass would be reduced to a 2” +/- particle size and be fed into a 75 HP biomass boiler. The use of a dual fuel boiler that can utilize biomass or oil could be utilized to allow either biomass or oil as the primary fuel source. The biomass plant would replace the proposed oil-fired boiler in the WTP as well as the purchase of thermal energy from KEA. However, to provide 100% redundancy, there will still be a 75 HP oil fired boiler installed in the WTP. Because of this, it is recommended to purchase the biomass boiler without the oil burner, since redundancy will be available at the WTP To provide the same level of heating as Option 1 would require approximately 1175 tons/year of biomass. This option will require the installation of hot water lines from the biomass plant to the WTP. These lines would serve both the water and building heating requirements. Interest rate Term Capital 4% 20 150,000.00$ Annual Payment for Capital $11,037.26 Oil 456,900.00$ Payment to KEA -$ Net Cost $467,937.26 OPTION 1 - OIL FIRED at WTP 55 Technical Memorandum 4 Option 3 – KEA Supply All Heating Requirements The use of the waste heat from the KEA generators could provide a viable option to supply all the thermal requirements of the WTP building. This option would require a dedicated hot water line from the KEA plant to the WTP. This option would include a 75 HP oil fired boiler at the WTP for redundancy. For KEA to become the primary heat supplier, a revised thermal supply contract would need to be executed. Option 4 – KEA Supply Water Heating This option would have the heating requirements of the water system supplied as it is now. The building heat would be supplied by boilers in the WTP. To supply this heat will require a 50 HP boiler. There will be a redundant 50 HP boiler as well. based on discussions with KEA, the current configuration should be able to supply all the water and loop make-up heating with the current installation. Interest rate Term Capital 4% 20 1,700,000.00$ Annual Payment for Capital $125,088.98 O&M $375,000.00 Debt + Operating $500,088.98 Avoided biomass cost -$58,700.00 Net Cost $441,388.98 OPTION 2 - BIOMASS PLANT OPTION 3 - KEA supply all heating needs Interest rate Term Capital 4% 20 546,000.00$ Annual Payment for Capital $40,175.64 Oil -$ Payment to KEA 319,800.00$ Net Cost $359,975.64 Interest rate Term Capital 4% 20 125,000.00$ Annual Payment for Capital $9,197.72 Oil 43,000.00$ Payment to KEA 186,300.00$ Net Cost $238,497.72 OPTION 4- WTP supplies building heat. KEA supplies raw water and loop loss heat. 56 Technical Memorandum 5 In all options, the payment to KEA is based on the structure of the current contract. All calculations are based on a cost of oil of $4.62 per gallon and utilize the calculated heat loads shown in Attachment 1. DEVELOPMENT OF HEATING PLANS Following review of the data and proposed options with the City, it is proposed that the more specific designs and costs be developed for each option agreed upon. 57