By Mark Wheeler and Christopher Molnar
Medium voltage technology greatly reduces installation, operating, and maintenance cost for a multitude of thermal processes throughout an entire facility.
Most industries use low voltage systems, typically less than 700V, for electric heating applications. These were practical for most of the 20th century. Now, however, certain applications in such heavy industries as power generation, oil and gas, petrochemical, chemical, and others demand much higher power output. These applications require multi-megawatt (MW) electric heating systems. At low voltages, such requirements lead to challenges with power distribution, process design and costs.
A viable solution: moving to medium voltage. A safe and reliable technical design for metal-sheathed electric process heating now exists for heating systems operating at medium voltages. These patent-pending systems allow industry to capture all the advantages of electric process heat while minimizing the disadvantages of low voltage, high amperage designs. This article discusses the benefits and cost savings associated with heating systems operating at 4160 volts relative to traditional low voltage designs.
Medium voltage technology permits operation of process heat equipment directly off of an existing 4160V distribution system, potentially eliminating the installation of dedicated step-down transformers for low voltage duty. When operating multi-megawatt systems, this cost avoidance can be substantial, conservatively estimated in the neighborhood of $25,000 per MW installed.
Additionally, medium voltage technology for electric process heating drastically reduces the amperage draw for the same heat output. For example, operating process heating equipment at an industry standard 4160V reduces amperage by a factor of nine. This allows the end user to reduce both the wire diameter and number of wires necessary for installation when compared to a low voltage source. At 4160V, a conservative estimate of the material savings on wire alone can equal $1.50 per amp per foot of run. A multi-megawatt system operating at 4160V installed several hundred feet from the main distribution bus can instantly save the end user close to $200,000.
Finally, the higher voltage decreases the labor cost necessary for installation. Using fewer wires of smaller diameter greatly reduces the time and effort for installation. At 4160V, the estimated labor savings on wire installation costs about $0.15 per amp per foot of run. Although dollar savings based on a conservative situation yield about $15,000, installation time drops by a factor of 10, decreasing wire and conduit labor time from weeks to only days. This obviously helps to decrease the overall project timeline and cost.
Operating at medium voltages increases the efficiency of power distribution and consumption. Although electric process heat and control solutions have much higher efficiencies than fuel-fired systems, especially at reduced duty cycles, they are still not perfectly 100% efficient. Energy losses occur in the form of heat generation, often designated as I2R losses. A typical low voltage system will operate at about 96% efficiency, with 4% energy loss coming from heat generated by current transmission across wire, bussing, connections and instrumentation.
However, the lower amperage associated with medium voltage technology minimizes heat loss for a given power output. This is why electric power transmission lines operate at hundreds of thousands of volts — for high efficiency line loss reduction. For example, a multi-megawatt process heating solution operating at 4160V will run at almost 99% efficiency. That 3% improvement in efficiency translates into operating cost savings for the life of the system. For example, assuming a cost of $0.05/kWh from your utility, an end user will save tens of thousands of dollars every year of operation. With a life expectancy of 20 years or more, this is significant.
Another possible advantage results from incentives by many electric utilities that reward reduced consumption. These incentives permit the end user to receive a lower price rate from the utility, or a grant or rebate to help pay the capital costs for the investment of the medium voltage equipment.
One key advantage of electric process heat in general is the low cost of maintenance. With no moving parts and a robust design, electric process heaters will often operate for decades with minimal maintenance relative to fuel-fired equipment. And although the major parts of an electric process heater do not require regular adjustments, routine inspections of electrical connections help to ensure safety and minimize inefficiency from losses. The fact that medium voltage technology requires fewer wires and connections simplifies inspection time.
Often electric heaters in heavy industry operate in process-critical situations where downtime can cost hundreds of thousands of dollars, if not millions, a day. So failure of a heating element can be a major cost factor. Regardless of the cause, the impact to an end user’s operation can be catastrophic. End users must make decisions regarding their source of replacement heating bundles: whether sourced as needed or stocked for emergencies.
For critical process situations, the end user may choose to purchase a spare heating bundle along with the original equipment. This can add as much as 50% to 60% to the entire system cost. The alternative is to source a heating bundle as needed, which can result in a significant lead time and/or cost for expediting. These alternatives can be costly, time consuming, and unpredictable.
According to the authors, the system that incorporates replaceable medium voltage elements mitigates that cost and risk. The end user can purchase a low cost set of spare elements for on-site storage. Should an emergency arise, the cost and production downtime for replacing the failed elements is greatly reduced. For a typical multi-megawatt system, the cost savings associated with replaceable elements can reach $100,000 per incident. Downtime may drop to a matter of days as opposed to many weeks for a sourced replacement bundle.
About The Authors
Mark Wheeler, Global Director of Systems and Service, and Christopher J. Molnar, Vice President of Industrial Heaters and Systems, bring years of experience to the innovative team at Chromalox, Inc. Mr. Wheeler is a veteran in the field of advanced thermal technologies, working with customers on a global scale to develop solutions to the most difficult and unique heating challenges. He has 17 years of experience in precision heating with a focus on developing customized solutions for new plant installations and expansions. Notably, Mr. Wheeler and his team have secured an explosion-proof certification and design patent for tank fledged immersion heaters and introduced DirectConnect as part of its extended technology platform.
Mr. Molnar is a veteran in the field of delivering process heating solutions for revenue-generating industrial processes with several patents to his credit. A member of Chromalox’s professional staff since 1997, he holds a B.S. degree in Mechanical Engineering from Grove City Collete, a M.S. degree in Mechanical Engineering from the University of Pittsburg, and an MBA from Carnegie Mellon University – Tepper School of Business.
Both Mr. Wheeler and Mr. Molnar are located at the Chromalox, Inc. headquarters at 103 Gamma Drive in Pittsburgh, Pennsylvania. They can be reached at 412.967.3800.