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2008 10 09 Fire-Tube Immersion Heater Efficiency Improvement Design Guideline Project
BackgroundThe Upstream Oil and Gas Industry is an energy intensive industry. The industry is required to consume significant amounts of energy to process raw gas and liquids to either a finished or semi-finished product of sales gas, LPG's, sulphur and oil or condensate. This energy requirement is commonly referred to as the Production Energy Intensity (PEI). One specific area that is of common concern to many upstream operating companies is the energy consumption associated with fire tube immersion heaters. The energy frequently used to fire these heaters is high-quality refined sales gas. In 1979, a study estimated that in Alberta line-heaters and treaters consumed 70 Bcf/A in fuel gas, which is equivalent to 8 billion BTU/hr, at a cost in excess of $320 million/A. A common problem with the immersion heaters is that individual heaters generally have low fuel efficiencies between 30% and 60%. Compared to common boiler technology, these heaters should be able to run at between 70 to 80% efficiency. Even when taking into consideration the cyclic nature of operation associated with many of the applications, these heaters currently waste in excess of 2 to 3 billion BTU/hr of fuel (1360 to 2040 e3m3/d gas) that could be conserved to generate added sales. At an average cost of $5/GJ this represents $100 to $150 million of lost revenues due to inefficient use of fuel gas. This also represents an associated 1.5 million additional tonnes of carbon dioxide being discharged into the atmosphere per year. Often lower heater efficiencies are associated with high levels of oxygen or combustibles and high stack temperatures. These can result from poor burner performance and poor control of combustion air or improper configuration or the size of the fire-tube. Unlike steam or hot water boiler practices of efficiency calculations and/or guarantees, the efficiencies of immersion heaters are rarely considered during the typical specification, design, manufacturing, or operation cycle of the equipment. A study was commissioned by PTAC's TEREE Committee to examine improving the efficiency of Fire-Tube Immersion Heaters ("Improved Fire-Tube Immersion Heater Efficiency Project") which was carried out by ENEFEN Energy Efficiency Engineering Ltd. And completed in August 2005. The principal objective of this project was to define practical methods for increasing energy efficiency and reducing emissions of gas fired immersion fire-tube heaters used in the petroleum industry. In addition, these methods were designed, to provide the improvement to the largest number of both the existing heaters, and new installations, at the lowest cost and with a minimum of modifications. This project identified an achievable theoretical target gross efficiency for fire-tube heaters at between 72% and 82% depending on the bath liquid temperature. To confirm these efficiency targets, a detailed survey of 43 field installations in various applications was conducted, and eight installations with efficiencies as low as 30% were found. Simple readjustment of all eight of these units during the survey returned them to higher efficiencies between 64% and 82%, with an average efficiency of 72.3%. This part of the project also produced guidelines and data collection methods for evaluating fire-tube heater efficiencies in the field. A review of immersion heater design practices was undertaken to assess the impact and applicability of the commonly used design values of 10,000 BTU/hr/ft2 and 15,000 BTU/hr/in2 for the surface and cross-sectional heat flux rates, respectively, on the heater efficiency. The analysis showed that with a 2-pass design in line heater application both of these values are almost guaranteed to produce heater efficiencies lower than the 72% low efficiency target. Instead of using these traditional design values a more accurate assessment can now be performed using the fire tube rating charts and the fire-tube rating software generated as part of this study. A very important aspect of both existing and new installations is that many of them are already, or very likely will become, oversized for the actual process energy requirement, due to decline in production volumes. If these heaters were fired at duties less than design, the extra surface of the fire-tube would improve the heat transfer, as well as, reduce the typical ON/OFF cycling to a more consistent operation. This approach offers an excellent opportunity for energy savings with minimal modification to the existing heater. Although a standard engineering solution to this problem would be to use a conventional method of burner fuel modulation, this study shows that this method is ineffective without addressing the secondary air control. This can be achieved without any mechanical means, simply by utilizing natural characteristics of the Venturi style burner. The general concept of maximizing the efficiency of the fire-tube heater is by the proper matching of the fire-tube configuration, burner size and design, and modulating controls, without shutting the heater down and while maintaining its low excess air operation (between 2% and 3% oxygen in the stack). Additional energy efficiency measures were identified, including: turning the pilot OFF; eliminating the instrument gas powered pneumatic controls, and using solar power to operate heater controls. The research described in this study also led to a conclusion that energy efficiency issues related to the fire-tube heaters often go beyond the technical aspects of fire-tube sizing, burner selection or controls design. The operational and maintenance aspects, and concerns about heater reliability, availability, and safety also influence them. These concerns often overrule the requirements for higher efficiencies and lower emissions. The study contains information, design tools, evaluation and maintenance guidelines, as well as, both engineering and organizational concepts and recommendations, which could be used to solve the fire-tube heater energy efficiency and emissions challenge on an industry wide scale. One of the recurring topics of this research is the need for education related to the energy efficiency of the fire-tube heaters. This study proposes the development under the auspices of PITS of an industry and government sanctioned sub-trade, which would provide a suitable knowledge base in the industry, to properly install, operate, and maintain thousands of high efficiency fire-tube heaters. This Request for Proposal is for the development of a "Design Guide" for Immersion Fire Tube Heaters for the conventional upstream oil & gas industry, based on operational and design data previously developed and reported in the TEREE Committee Phase 1 study, "IMPROVED IMMERSION FIRE-TUBE HEATER EFFICIENCY PROJECT", carried out by ENEFEN Energy Efficiency Engineering Ltd. The benefits to undertaking the development of this Design Guide to industry and Canada include the following:
RequirementTaking into consideration rising fuel costs and more stringent environmental regulations, there is a requirement by the industry for improvements in the design, evaluation, operation and maintenance practices leading to better operation and higher efficiencies of immersion fire-tube heaters. While the TEREE Committee Phase 1 study, "IMPROVED IMMERSION FIRE-TUBE HEATER EFFICIENCY PROJECT", carried out by ENEFEN Energy Efficiency Engineering Ltd. provides detailed first principles design information, field survey data, bench test performance data, fire tube rating design charts, analysis of surface and cross-sectional heat flux rates, guidelines for fire tube heater efficiency and reliability improvements, the report at roughly 450 pages is daunting to approach and extract usable information for use by design and operations personnel. Thus, a project has been initiated to undertake the development of a "Design Guide" for Immersion Fire-Tube Heaters for the conventional upstream oil & gas industry, based on operational and design data presented in this report. This guide should be considered as a complementary document to the "Best Management Practices" for the operation of Immersion Fire Tube Heaters, which has been developed by CAPP for the industry. Project SponsorsDeveloping new design guides, while sharing the development costs and operational support, is essential to improved efficiency projects. The funding organizations supporting this project include:
ObjectivesThis Request for Proposal is for the production of the following Guides for Fire-Tube Immersion Heaters:
Scope of WorkThe guide will not address all possible design parameters, or all possible operating conditions, but should provide a systematic approach and useful benchmarks to enable competent designers and operators to assess their particular design requirement or operating situation and identity methods for improving the efficiency of operation of immersion fire-tube heaters for which they are responsible, without sacrificing operational safety or unit reliability and availability. The guide will be generated from data presented in the PTAC TEREE Phase 1 report, and will be subjected to review by industry members on the TEREE committee before being "Accepted' by TEREE. The guides will also be limited to the sizes of equipment referenced in the original report. The Design Guide should be more than a summary of issues taken from the TEREE Phase 1 report, but should also define design protocols based on key design and performance characteristics of immersion fire-tube heaters. For example, a fixed schedule of heater designs could be proposed, such as defining line heater configurations from 0.25 mmBTU/hr to 10.0 mmBTU/hr process duty with potential options in single or multiple tube fire-tubes in larger heaters for turndown. Another example of how the Design Guide might influence fire-tube immersion heater design would be to offer alternative design approaches such as moving from 10,000 BTU/ft2 heat flux to 7,000 BTU/ft2 heat flux designs and specifying the shape of the fire-tube (i.e. the slope and turndown expectations before condensing, which is a different approach from simply defining length to diameter aspect ratios). The operational impacts of such design recommendations would also need to be described (that is for the given example of a 7,000 BTU/ft2 heat flux design), at start-up the heater could be fired at 10,000 btu/ft2 to warm up a well and flowline but once up and stable trim out at 7,000 or less for efficiency but to avoid condensing. The proponent for the work may also recommend the development of software tools as part of the guidelines package, but the costs for these software developments should be identified separately from the work to develop the Guides/manuals. Scope of Work - Design GuideThe Design Guide for Improved Efficiency of Fire-Tube Immersion Heaters should, for example, extract and organize the following information from the original report: Design Methodologies for New Equipment
Design Methodologies for Operational Field Equipment
DeliverablesThe deliverables for this project shall include the following Guide for the design of Fire-Tube Immersion Heaters:
The Guide or manual should focus on recommended approaches identified in the ENERFEN report, but may include additional input and insights from proponents or industry sponsors as the work is reviewed. The guides may include software to aid, in particular, the design approaches to improve fire-tube heater efficiency, but should be identified as a separate deliverable in the proposal to TEREE. ScheduleThe project, based on the scope described will fall into two stages:
Milestones and deliverables for the project
BudgetThe anticipated budget for the work is as follows:
Total Cost: $60,000 Note: Not included in this budget estimate is the in-kind contribution of industry members' time to participate in and review the outcomes of this project. Contact InformationPreliminary proposals should be submitted via email to Susie Dwyer of PTAC at sdwyer@ptac.org, 403-218-7708. EOIs should be faxed to Susie at 403-920-0054. The RFP and other related documentation will be available on PTAC's website at www.ptac.org or from Susie Dwyer. PTAC is the neutral facilitator of this RFP and PTAC staff will not screen, evaluate or make decisions on what will proceed. Technical questions should be emailed to Soheil Asgarpour at sasgarpour@ptac.org or 403-218-7701. PTAC is an association that facilitates innovation, collaborative research, and technology development, demonstration and deployment for a responsible Western Canadian upstream hydrocarbon energy industry.PTAC'S objective is to improve the industry's financial, environmental and safety performance through the application of new technology and research. More information on PTAC is avalable at www.ptac.org. PTAC launched the TEREE project in 2003 to facilitate technologies that will reduce the industry's impact on the environment, while improving profitability and eco-efficiency. More information on TEREE, including the terms of reference is available athttp://www.ptac.org/techeetteree.html DISCLAIMER PTAC is only a facilitator for these presentations. PTAC makes no representation regarding ownership or quality of any technology described by a presenter, or generally as to the contents of a presentation. PTAC does not endorse any presenter nor the technology presented. Please use your own judgment. PTAC trusts that each presenter will engage in fair trade practices, but does not police or otherwise enforce this policy in any manner. |
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For further information, |
Susie Dwyer, PTAC |
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© PTAC 2008 |
2008 10 31 LF |
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