Biomass is a plant-based product used as fuel to generate heat and electricity. It is an eco-friendly renewable alternative to traditional forms of energy, such as fossil fuels. Biomass includes wood products such as chips, logs, pellets, and other forestry materials such as limbs and brush.
Biomass-fired combustion systems are useful in many wood product manufacturing and power generation processes. These systems are commonly used for hot gas generation and indirect heating applications. Some applications include:
Rotary Dryers – Flue Gas Generation from Combustion
OSB, Belt Dryers, ORC, and Misc Secondary Users – Heating Thermal Oil
Steam Turbines – Steam Boiler
Sigma Thermal is a leading provider of modern furnace systems fired by biomass. Our engineering experts provide logistics, troubleshooting, custom maintenance, and related equipment for world-leading industrial contractors. Learn more about the importance of fuel moisture, recommended fuel specifications, and proper inspections for biomass fuel systems.
Importance of Fuel Moisture
Fuel moisture is the water content present in the fuel, represented as a percentage. Moisture content matters in solid fuels because it influences burning behaviors. If the biomass has too much water moisture, it may not burn all the fuel or as easily and produces no energy or less useful heat energy relative to unit mass. It can also cause excessive amounts of carbon monoxide which comes from incomplete combustion. If the biomass is too dry, it can reach ash fusion temperatures, foul the heat recovery equipment, or pose an explosion risk.
Because of these challenges, water content of the biomass must fall within a certain range to be most effective. Sigma Thermal’s reciprocating grate furnaces operate ideally with fuel moisture between 35% to 55%. It is important to size the grate floor of the furnace properly according to the maximum percentage of moisture the plant will be burning.
Equipment operators must also understand the roles of primary air zones, secondary air, and flue gas recirculation (FGR). Primary air is the amount of air used in the lower furnace to initiate combustion and controls the quantity and speed of fuel burned. Secondary air enables mixing of combustion gases and fresh air, completes the combustion, and allows the fuel to burn completely, which means combusting all of the carbon in the fuel making the combustion process more efficient.
The amount of secondary air you need depends on the firing rate and the moisture in the fuel. If the fuel is dry, more secondary air is needed to quench the combustion temperature and vice versa. If the fuel contains higher moisture, then less secondary air is needed. FGR is a technique that significantly reduces nitrogen oxide (NOx) emissions by recirculating flue gasses into the combustion chamber. This technique lowers flue gas temperature and oxygen content in the combustion mixture.
Moisture coming into the system must be consistent; operators should be aware of drastic fuel moisture swings, as these extreme changes can cause loss of control of the combustion inside the furnace and make the overall fuel usage go up while actual conversion of carbon-to-carbon dioxide goes down. This would mean the process is less efficient and not all of the fuel gets combusted.
Wet vs Dry Fuel
Lower Heating Value
Higher Heating Value
Must Burn More Mass
Burn Less Mass
Need more Drying time
Need Thicker Bed
Need Less Combustion Air & Secondary Air
More Secondary Air or Recirc Air for Cooling
Lower Combustion Temperatureand Potential for more CO
Watch for Glassing
Particle Size Consistency
Particle size consistency is another crucial factor in biomass combustion systems. For 100% bark fuel, particles should not exceed 6 inches, and particles in 90% bark content should be no more than 4 inches. The sizes vary further depending on different types of fuel content. Regardless of the type of biomass, fines—very small, fine particles—pose a variety of issues, including:
Buildup and glassing
Bed becomes difficult to maintain
High flame temperatures
The wrong balance of primary and secondary air can also aggravate problems arising from particle size inconsistencies. For example, too much primary air can cause high velocity through the grates, which increases carryover of fines. Not enough primary air can result in unburned fuel being dumped off the grates and other production inefficiencies.
The presence of excess fines usually means moisture content is too low, usually under 40%. To resolve the issue of too many fines, operators should first decrease the flow of primary air and then increase secondary air or recirculate to the quench chamber. Under-fire air dampers in zones 1 and 2—the main drying chambers—should be reduced in 3-5% increments but should not dip lower than 10%. The fire line will slowly move down the grate. If the bed is thin, operators can then increase fuel feed rate.
Recommended Fuel Specifications
Sigma Thermal’s reciprocating grate furnaces are designed to burn biomass with high ash content, low heating value, and high moisture content. The design allows finite combustion control that minimizes emissions and uses fuels with unique fuel particle sizes, chemical compositions, and moisture content. Larger percentages of fines can cause high flame temperatures, large volumes of unburned carbon in flue gas streams, glassing, and difficulties maintaining bed thickness.
In fuel analysis testing, there are important factors to consider, including:
Fuel particle size distribution
Carbon and hydrogen content
Ash fusion temperature
Different world regions have varying standards for biomass furnaces, so check your local regulations before implementing a system in your facility.
Furnace inspection involves checking the condition of all essential components, such as grate bars, refractory, moving frame roller tracks, emergency stack, fans, and dampers. It also includes cleaning, testing, and lubricating any moving parts.
The following are signs of an improper operation:
Cracked bars: These indicate rapid temperature changes and rapid contraction of the alloy steel, typically from a water
Warped bars: Warped bars result from high flame temperatures and oxygen concentrations.
Holes in bar nose: This damage is due to wear and high temperatures.
Refractory damage:Large amounts of glassed material in the upper furnace are a sign that the operating temperature in the furnace has been too high. In extreme cases, the refractory anchors can overheat and conduct heat back to the furnace casing, where the anchor is welded to the wall. This will lead to refractory failure.
Biomass Fuel Systems from Sigma Thermal
Sigma Thermal provides complete biomass fuel system solutions. We understand what it takes to design, engineer, and manufacture efficient, high-performance systems. Our products include indirect process bath heaters, direct-fired process heaters, thermal fluid heating systems, electric process heaters, biomass-fired energy systems, and more. Contact us for more information, or request a quote to start your solution today.
Pressure vessels are containers used for holding gases, vapors, or liquids with pressures above or below the ambient pressure. Since the vessels operate under pressure in industrial applications, their fabrication must adhere to a strict code of construction, including the ASME code — also called the ASME Boiler & Pressure Vessel Code or BPVC.
ASME, short for the American Society of Mechanical Engineers, is one of the leading authorities that regulates pressure vessels and boilers. At Sigma Thermal, we uphold exceptional design and quality standards for all of our products, as evidenced by our adherence to ASME requirements.
Types of Pressure Vessels
There are two main types of pressure vessels used in thermal fluid systems:
Heat Exchangers: Heat exchangers enable heat transfer between fluids while preventing direct contact between them. Popular applications of these systems include energy, food, bioprocessing, and pharmaceutical industries. Most heat exchangers have a series of metal tubes where one product flows through while the other flows around the tubes allowing heat exchange to occur.
Fluid Heaters: Fluid heaters are closed vessels that facilitate the exchange of heat from an electrical or fuel-based source to the heat transfer fluid. These systems are used to heat liquids directly or indirectly.
At Sigma Thermal, we primarily use carbon and stainless steel to manufacture our pressure vessels. However, we can construct pressure vessels using other materials approved in the ASME Sect. II part D.
Below are design aspects to consider when building a pressure vessel:
Calculation of vessel specifications occurs around the design pressure, a value obtained from the maximum operating pressure expected during startups, emergency shutdowns, process abnormalities, and other upset conditions. Design pressure should be 5-10% above the maximum operating pressure. If the vessel has the likelihood of experiencing vacuum pressure, the design pressure must be a value that resists a full vacuum (-14.7 PSIG).
The maximum allowable pressure depends on the temperature because material strength may be lower with increasing temperature, and material toughness may be lower in low temperatures. Pressure vessels should not operate at a temperature above the evaluated maximum allowable stress value. Therefore, the design temperature is always less than the minimum temperature and greater than the maximum operating temperature.
3. Corrosion allowance
Corrosion allowance requirements may vary by manufacturer or engineering specifier. Heat exchanger equipment specifically requires a small corrosion allowance because wall thickness affects the heat transfer rate.
4. Allowable stress
The maximum allowable stress of a pressure vessel is determined by ASME Section II part D. The stress values in ASME Section II part D account for potential deviations from the ideal construction and operation of the pressure vessel.
5. Joint efficiency
Another thing to consider in pressure vessel design is joint efficiency. Joint efficiency refers to the ratio of the strength of the welded plate to that of the unwelded plate. Joint efficiencies are determined by the ASME BPV Code Sec. VIII D.1.
Design Considerations for Pressure Vessels Related to ASME
Importance of ASME for safety and quality
ASME standards provide guidelines that help prevent accidents by making pressure vessels safer. Therefore, ASME certification is an accreditation that a piece of equipment adheres to the ASME code. Having a pressure vessel with an ASME stamp is an assurance that is proven to comply with the quality and safety standards of the Boiler and Pressure Vessel Code.
Requirements of ASME
ASME codes cover everything, including the design, creation, maintenance, and adjustments of pressurized equipment. Pressure vessels, heat exchangers use ASME code VIII-1, while hot water heaters and boilers use ASME code I. The design by rules codes give formula methods that work if the design falls clearly within the range of the code.
Thermal Fluid Heating Systems From Sigma Thermal
At Sigma Thermal, we have years of experience designing and manufacturing ASME code-compliant thermal fluid heating systems. We are proud to offer our customers with high-quality heating solutions they need to maintain seamless and efficient operations in their plants. Contact us today to learn more or request a quote and our representatives will get in touch with you.
Waste heat recovery systems help manage, recover, and repurpose waste heat from various energy consuming systems in commercial, industrial, and municipal facilities. As machines run, processing systems prepare goods or products, they often put off heat as a waste product. That waste heat is typically either a result of the friction of moving parts or from the exhaust of various types of combustion equipment. While the heat of friction can be significant, waste heat from exhaust streams is typically the most practical to recover and utilize. Repurposing waste heat allows facilities to become more efficient, reduce thier fuel costs, and overall emissions to the environment.
How Do They Work?
Click to Expand
One of the most common types of waste heat recovery systems is a closed-loop liquid phase system filled with a thermal fluid of some type: typically thermal oil or a water/glycol solution. Within a waste heat recovery coil located in the exhaust stack or in the exhaust gas ductwork, the circulated thermal fluid absorbs the waste heat from the exhaust stream. The heated fluid is then circulated to the the chosen waste heat consumer(s) within the closed-loop system, where it will offset the heat demand of the combustion system providing that particular system with its heat energy.
The challenge for the system designer is to match a heat energy consumer with a waste energy source. In order for the system to work the waste heat source must be hotter than the heat consumer with enough margin to drive the heat transfer from one system to the other. One of the biggest benefits of a closed loop liquid phase heat recovery system is it’s ability to connect multiple sources with multiple consumers that may not be physically close to one another. If, for example, if three exhaust stacks in one part of the plant collectively produce 450F exhaust, and a boiler feedwater system 200 yards away could utilize that waste heat to pre-heat the feedwater to 200F, the energy can be collected from the three sources, combined, and then circulated over to a feedwater heat exchange to heat the boiler feedwater. The cold thermal fluid simply recirculates from the heat exchanger outlet back to the waste heat sources, and the process repeats continuously.
Benefits of Using Waste Heat Recovery Systems
Manufacturing centers, processing facilities, and large buildings all benefit from the introduction of closed-loop waste heat recovery systems. Some of the core benefits include:
Because the systems recover heat energy the facility has already generated, the facility can use that energy more intentionally instead of having to pay for heat that is rejected to the environment. Recovering energy can reduce operational costs by offsetting energy demand, and therefore fuel consumed, in gas or oil fired combustion equipment. Natural gas and/or diesel fuel costs can fluctuate and can be a significant portion of a plants total energy operating costs.
Waste heat boilers are often utlized as altneratives to closed loop liquid systems, but they can actually be less efficient to operate. Steam traps, blow down, and energy lost to condensate return cause inneffeciencies in the system that don’t exist in a closed loop liquid phase system. For those reasons, a closed loop liquid phase waste heat recovery system may allow you to utilize more of your waste heat and maximize your fuel cost offset.
In addition to fuel cost savings, there are frequently opportunities for government funding, tax credits, and other incentives at the federal, state, and local levels. These can be specific to waste heat recovery projects, or generalized incentives for sustainability and effeciency improvement initiatives. In many cases there are several incentives available at multiple levels that can all be utilized in tandem with one another: federal, state, and local. These incentive can significnat decrease the cost of installing a system, decreasing your investment payback period and maximizing your long term cost savings.
Waste Heat Recovery Systems From Sigma Thermal
At Sigma Thermal, we have the experience and expertise to design or select the right closed-loop waste heat recovery system for your facility’s needs. Our company is ISO 9001:2015-certified, and our signature process includes every step from initial system design to installation and complete project management. Contact us today to learn more or request a quote to start your project.
Pre-Engineered Thermal Fluid Systems vs. Custom Thermal Fluid Systems – How to Decide What You Need
Depending on the needs of a particular application, either a pre-engineered thermal fluid system or a custom-engineered thermal fluid system may be ideal. In this blog post, we’ll cover the differences between these two types of systems to help you determine which is best for your application. Both feature unique benefits, which is why it’s important to understand their differences when deciding which to use for your project.
Pros and Cons to Each Heating System
When selecting a thermal fluid system is critical, it’s important to:
Define the application’s unique performance requirements
Thoroughly assess the installation requirements and any specific facility needs
Compare different thermal system suppliers and learn about their products and how they approach projects for their customers
Determine how to properly install and operate the system in your facility
Keep in mind that any mistake made in these areas may negatively impact your project. Whether you fail to assess the different heater designs or don’t take the time to compare suppliers, these and other mistakes are difficult to correct once you start installing your system. Fortunately, Sigma Thermal is here to provide plenty of guidance to ensure you make the right decisions regarding your thermal fluid system.
One key decision you’ll need to make during system selection is whether to use a pre-engineered system, a custom-engineered system, or a combination of the two. To help you make this critical decision, the following are some of the pros and cons of each type of system.
Reduced capital cost due to standard bill of materials
Faster delivery times because no engineering is required
Fully defined dimensions, drawings, and performance prior to purchase
Simplified projects and reduced site or plant engineering expenses due to the lack of drawings that require review, revisions, or approval
Custom Engineered Thermal Fluid Systems
On the other hand, custom thermal fluid systems are often a better choice for more complex installations or processes. You may want to implement one of these systems if you plan to provide guidance on or specify certain factors such as:
For custom engineered thermal fluid systems, you should provide information regarding the following process considerations:
System flow rates
Fuels, including biogas, waste gas, liquid fuels, off-spec fuels, variable fuel compositions, or dirty fuels
Strict requirements for emissions
Heat transfer fluids such as silicone-based fluids, molten salt, or ultra high-temp synthetic oils
Review and Approval of Drawings
In some cases, you may want to directly influence:
Connection location and orientation
Mechanical specifics such as configuration, materials, and paint
Certain system components if your company has required specific instruments, valves, pumps, or other buy-out equipment.
Factory interconnection and skid mounting for various components, such as mounting an expansion tank, pump skid, heater, and drain tank on one skid frame
Custom secondary loop skids for auxiliaries such as indirect steam generators, temperature control units, control valves, and process coolers
A Hybrid Approach – Mixing and Matching Pre-Engineered and Custom Components
At Sigma Thermal, we offer a modular approach to pre-engineered thermal fluid systems, which facilitates the combination of both pre-engineered and custom-engineered systems. Using this hybrid approach, you can use pre-engineered components for areas that don’t require customization. At the same time, you can customize the specific areas over which you want more control. If, for example, you can use a pre-engineered heater and pump skid design, but you have a large system volume and need a large custom expansion and/or drain tank, you could take a hybrid approach to the system design.
Using a hybrid approach to system selection, you can save more time and cost while simplifying your systems. Additionally, you’ll be able to easily adapt systems for specific project requirements.
Process Heating Systems from Sigma Thermal
The experienced professionals at Sigma Thermal specialize in pre-engineered and custom-engineered thermal fluid heating systems. Our equipment allows for optimal installation, operation, and fulfillment. If you require pre-engineered thermal fluid systems, we offer both our HC2 gas-fired heaters and SHOTS electric heaters. We can also work with you to design a completely custom solution if you want to specify certain components and design elements.
For additional information about our thermal fluid systems, contact us today with any questions or concerns. We can also help you find the ideal solution when you request a quote from us.
With decades of global experience in the energy industry, Sigma Thermal knows how to provide robust industrial solutions designed and engineered to meet even the most demanding client specifications. Our biomass fired energy systems provide minimal emissions and finite combustion control, all while accepting a wide range of waste fuels with varying sizes, chemical compositions, and moisture content.
Sigma Thermal’s reciprocating grate furnace allows for the efficient, complete combustion of waste materials with high ash, high moisture content and low heating value. Keep reading for more information about how these systems work as well as the different energy delivery systems that we offer.
How Does a Biomass System Work?
Biomass energy systems all generally consist of three components—fuel handling, ash handling, a furnace, and a control system. Biomass equipment employs these four systems to convert raw organic material into fuel in a series of steps:
Fuel preparation. Before biomass equipment can effectively handle raw material, it must process and prepare the biomass used for fuel production. Solid, liquid, and gas biomass all require different processing techniques to ensure consistency and efficiency, such as drying, screening, grinding, and separating.
Fuel intake and handling. The fuel handling system includes the initial feed and an intermediate storage bin. Fuel moves from the feed to the storage bin, where specialized equipment measures it out and subsequently distributes it into the furnace and onto the reciprocating grate.
Material combustion. Biomass energy systems heat and combust the prepared materials with process heating equipment, achieving drying and gasification by creating hot gases that will move along through the next steps of the process.
Gas capture. Newly created hot gases move through two chambers, the upper combustion chamber and the secondary combustion chamber, which capture and store the gases for future use. Burning biomass for energy generates carbon dioxide as a byproduct, so proper gas capture and removal is crucial to keeping carbon emissions low.
Ash handling. Lastly, the ash handling system captures the grate ash byproduct, which is dropped from ash hoppers to the ash conveyor. This conveyor is submerged underwater for improved ash management and transports the ash outside of the system where it can be collected and disposed of.
Energy Delivery Systems & Equipment for Enhanced Performance
Bio energy systems provide several benefits over traditional energy generation solutions, including enhanced performance, efficiency, and more. Biomass fired energy systems are a source of renewable energy, which makes them eligible for a host of benefits like Renewables Energy Certificates (RECs) for each MWh of power created or even process heat RECs. . Not only is biomass renewable, but it also boasts carbon savings that have both environmental and financial benefits, especially in the industrial sector.
Biomass energy delivery systems are also incredibly efficient regarding total cost and material usage. Advanced gasification technology like the processes described above can have up to 80-90% thermal efficiency, which drastically reduces input costs and expands profit margins. Operational fuel cost savings and reduced fuel price volatility are other key benefits of biomass energy since organic waste energy sources are much more available and abundant than nonrenewable sources of fuel. Finally, biomass fired energy is considered an efficient combined heat and power (CHP) system as it simultaneously generates both heat and electricity.
At Sigma Thermal, we offer several different types of energy delivery systems:
Biomass Fired Hot Gas Generators. These systems cleanly generate hot gas for direct heating requirements.
Biomass Fired Thermal Fluid Heaters. Built for indirect heating, these systems use thermal oil or fluid.
Thermal Oil to Steam Generation. These systems use a thermal oil heat exchanger to generate low-pressure steam.
Let Our Process Heating Experts Assist You
Partner with our team of industry veterans to unlock the benefits of bio energy systems. From highly engineered process heating equipment to standard packaged heaters, Sigma Thermal’s dedicated experts know how to find the perfect biomass energy systems for your individual needs. We believe that successful energy delivery systems require not only advanced industry knowledge and applied field experience but also exceptional customer service every step of the way. These three keys to success bind our team together and provide a powerful framework for consistently crafting exceptional biomass equipment and processes.
Direct fired heaters use one of three possible methods for heat transfer:
Radiant–convective style direct fired heaters are a popular style of heater and are used more often than not. These heaters utilize a bare tube radiant zone in combination with a bare / finned convection section. The most typical configurations are vertical cylindrical, A-frame, and cabin style. Sigma Thermal offers all types of direct fired radiant–convective heater designs including API 560 compliant systems.
Convection style direct fired heaters provide the benefits of a direct-fired heater, but eliminates some of the drawbacks associated with radiant heat transfer. In specific temperature-sensitive applications, radiant heat transfer can be undesirable, as radiant heat transfer tends to be more harsh and unevenly distributed around the coil surface. To minimize the impact effect of the radiant heat transfer to the process coil, Sigma Thermal’s convection style direct fired heaters are designed to utilize a separate combustion chamber and flue gas recirculation. With this design, the combustion chamber temperatures are reduced to 1,400°F.
API 560 Heaters vs Non API Heaters
Convection or radiant-convective direct-fired heaters can be designed using API RP 560 guidelines and practices created for fired heaters used for general refinery service. These guidelines are established by the American Petroleum Institute (API). Typically if the application involves the direct heating of crude oil, API560/ISO 13705 standard design guidelines will apply. For almost all other applications (i.e. regeneration gas, thermal oil heating, water, glycol, and temperature gases), more optimal designs are available that lower the capital and installed cost, footprint, fabrication, installation time, and freight cost. A practical strategy to use to obtain an API-style design, without incurring unnecessary costs for irrelevant design elements (that are not useful for some applications), is to use API 560 as a guideline with key exceptions.
5 Applications for Direct Fired Heaters
Regeneration Gas Heating
Regeneration gas heaters remove unwanted moisture from high-temperature process streams, such as natural gas. The wet gas runs through a desiccant-style or molecular sieve bed drying system that captures moisture from the fluid stream, leaving a purer form of the gas that is ready for additional processing and storage. The regeneration gas heater then dries the desiccant so it can be reused. Regeneration gas heating systems are also common in air separation facilities, where water and carbon dioxide are removed from the surrounding air, allowing air to be cooled into a liquid.
Process Air Heating
Process air heating, in combustion turbine systems, improves combustion ability and the reliability of the system. Process air heating also temperature control for process air, either at specific locations or facility-wide. Common examples of this type of heater include water-glycol systems and thermal oil systems. Robust, reliable, and long-lasting, process air heating systems see frequent use for precision temperature control in commercial food processing ovens and feeding heated air into industrial process consumers.
Heating heavy liquids reduces their viscosity, reducing the level of power required to pump and transport them in process systems and pipelines. This process has become common to facilitate easier transportation of crude oil and its various derivatives. Overheating crude oil will damage it and reduce its quality, making precision control essential during viscosity reduction processes.
Skid-mounted indirect heating systems are often used near oil wells in remote locations, offering precision temperature control by heating oil through a heating medium. Some operations also use direct oil heating, which can be managed properly using low watt-density electric heating elements and convection-only style direct-fired heaters.
Inline Liquid or Gas Heating
In opposition to tank heaters or full process system heaters, inline heaters provide heat for fluids at a specific point in a process, making the fluid ready for its intended purpose. By only heating the gas or liquid that’s immediately needed, users significantly reduce energy consumption and associated expenses. Inline heaters may be either direct-fired or electric, depending on their intended application.
Thermal Oil Heating
Thermal oil heating systems provide indirect heating using thermal oil as a heat transfer medium. Thermal oil provides an ideal medium for high-temperature operation, facilitating temperatures up to 600°F with organic oils, or up to 800°F with synthetic oils. Thermal oil heating has broad applications, including reboilers, tank heating, press heating, and numerous other industrial use cases. Thermal oil heating systems work well for processes that require high-temperature operation and precision control.
Sigma Thermal Solutions
The above guide demonstrates the impressive versatility of direct fired heating systems. Whether you need to design a unit to suit one of the applications we’ve discussed here or an entirely new purpose, Sigma Thermal Solutions can produce direct fired heaters customized to your demands. Our business serves customers from an array of industries, including aerospace, agriculture, automotive manufacturing, chemical processing, food processing, gas production, mining, oil processing, power generation, paper manufacturing, wastewater processing, and more.
Our signature Sigma Thermal convection-style, API 560, and non-API radiant-convective heaters range from 1MM to 80 MM BTU per hour.To learn more about ordering direct fired heaters, contact an expert from Sigma Thermal Solutions today.
Sigma Thermal Solutions was founded on the belief there are three keys to success: exceptional engineering knowledge, practical field experience, and honest customer service. We look forward to helping you fulfill all your company’s heating needs!
Molten salts, also known as salt melts, comprise a variety of products that are used across many applications. Some applications that rely on molten salts include steel heat treating and annealing, high-temperature process heating, and thermal storage for solar thermal power plants. Depending on the needs of a specific application, different salts are available to use such as chlorides, bromides, fluorides, organic salts, and nitrates. Many applications use a eutectic blend of potassium nitrate and sodium nitrate.While there are several heat transfer fluid options available, molten salts are more ideal for certain applications due to the specific features unique to them.
Why Molten Salts?
There are several advantages of molten salts that make them appealing for use in a wide range of applications. The molten salts that are used most frequently in heat transfer applications are nitrate salts due to their low salt melting point, thermophysical properties, low vapor pressure, high operating temperature, corrosion performance, and low toxicity.
Molten salts help increase the maximum temperature limits in which a liquid heat transfer media can be utilized. Although individual salts are usable in these applications, combining two salts together helps reduce the melting point. The reduced melting point enables lower minimum operating temperatures, which minimizes the risk of freezing.
For example, the melting point of sodium nitrate is 584 °F or 307 °C, and the melting point of potassium nitrate is 631 °F or 333 °C. Combined, the two salts have a melting point of 431 °F or 222 °C. This melting point significantly expands the salt’s operational flexibility for use in various high-temperature applications.
If an application operates at temperatures exceeding 734 °F or 390 °C and requires a type of liquid heat transfer media, it will need to use a molten salt fluid.
Benefits for Industrial Applications?
A wide range of salt blends can help achieve specific operating temperatures required in certain applications. Compared to hydrocarbon fluids, molten salts experience minimal vapor pressure, regardless of how close operating temperatures are to their limits. As a result, high-pressure equipment and piping are almost entirely unneeded.
Molten salts are also usable at higher temperatures compared to other fluids such as silicone fluids and synthetic oils. They also have thermal stability and good heat transfer properties. Their high efficiency makes them suitable for use as heat transfer and molten salt energy storage media, as they are eco-friendly and can reduce operating costs.
Request Your Custom Molten Salt Systems
Depending on your application’s requirements, there are three main types of molten salt heating systems you can use. These include circulated molten salt, salt bath heaters, and direct heating for applications such as metal assembly heat treating.
At Sigma Thermal, we can provide:
Circulated molten salt systems that distribute hot liquid salt as a type of heat medium to process heat consumers such as heat exchangers.
Salt bath heater systems that use natural convection processes and eliminate the need for circulation pumps. This equipment is designed to operate at high temperatures to supply molten salt energy.
Sigma Thermal’s experts design and manufacture a variety of systems that use molten salt energy, including hot salt tanks, circulated molten salt systems, electric heaters, and salt bath heaters. We have the resources and experience needed to design fully automated custom systems. We can help you meet all of your process needs with our innovative solutions.
To learn more about our molten salt systems and get started on a custom solution for your specific application, request a quote today.
Certain types of heating systems, such as closed-looped thermal fluid heating systems, can use glycol to maintain heat transfer fluid to the desired temperature. While water is an ideal heat transfer medium for a certain range of temperatures, pure water has drawbacks. It can freeze below 32° F and it can corrode the internals of a heating system. Also referred to as antifreeze, glycol lowers the freezing temperature of the mixtures it is added to and it ensures that harsh weather conditions do not cause heating systems to freeze. In addition, glycol raises the boiling point of water to some degree, allowing for higher operating temperatures with less operating pressure than pure water. Glycol is also frequently purchased with corrosion inhibitors that reduce corrosion inside of the system over time.
Why Are Glycol Heaters Important?
Without adding glycol to a heating system, expensive and potentially dangerous damage to process equipment can occur. If the heating system is shut off for some time during the winter, the system and its pipes can freeze and burst, causing water damage. In addition to preventing system freezing, glycol mixtures are also a very efficient heat transfer medium compared to oils or water alone. Water and glycol mixtures have a better heat capacity than oils and perform well in many types of heaters. There are temperature limitations relative to thermal oils, but within the right range, a water-glycol solution is an excellent choice. Additionally, glycol heaters are valuable due to the safe heat transfer that they provide. For example, it can be dangerous to have heating elements near the process or materials, but using a glycol heating system keeps the heat source safely away from the process. Thermal oils are also a fire hazard if there is a system leak, while glycol solutions are not flammable.
Using Glycol in Industrial Heating System Applications
Ethylene and propylene glycol are commonly used in industrial facilities for process cooling. However, they are also used in process heating systems. They are very effective in heating applications due to several properties, such as:
High specific heat capacity
High thermal conductivity
Water and glycol solutions present many benefits for industrial processes, on the other hand, these are not the only heat transfer mediums available. Synthetic and organic thermal oils are also sometimes selected as they work well in temperatures up to 750° F and produce very little vapor pressure. Water without additives can also be used, although within more limited conditions due to its low-temperature intolerance and boiling point. It is also possible for water to produce a dangerous amount of vapor pressure at certain temperatures.
A water and glycol mixture can be a preferable choice in many applications since it has a higher boiling point than water alone, which can be increased further by including a higher concentration of glycol. Different types of glycol can be used for varying operating temperatures. For example, while ethylene and propylene glycol are suitable for systems with temperatures between 250–300° F, Tri-ethylene glycol works effectively up to 350° F.
Glycol Heaters from Sigma Thermal
Sigma Thermal’s glycol heaters, such as HC-2 heaters, are designed to meet all area classifications and can perform optimally in even the harshest of environments, including deserts, arctic, and offshore regions. The HC-2 thermal fluid heater is available in capacities from 1 to 100MM Btu/hr, with custom sizes also available. The heater shell is externally insulated using mineral wool insulation which is covered in aluminum cladding.
Some other design features of glycol heaters from Sigma Thermal include advanced control system options and a double-helical coil design, which offers three passes of flue gas along a conservatively designed coil surface area. Depending on process inlet temperatures, base efficiencies can exceed 88%, and by including an optional economizer, can exceed 93% (LHV basis).
These systems allow flue gases to be cooled significantly, which eliminates the need for most internal shell insulation. Sigma Thermal carries low emissions burners that meet all emissions requirements in standard or engineered burner configurations that can be used with either traditional or alternative fuel sources.
Sigma Thermal offers customizable glycol heaters that lower fuel and operation costs while improving efficiency. To learn more about our products, please contact us or request a quote to get started.