tube and fins heat exchanger

 

A tube and fins heat exchanger is an equipment designed to transfer energy from one stream to another through different systems, mostly air, exhaust gases, water, overheated water, refrigerants and steam.

Some of these elements may have demanding characteristics such as viscosities and sediments, in addition to working in corrosive environments.

Some of the main uses are:

Evaporators
Condensers
Cold water
Heat water

In this sense, Boixac Tech offers tailor-made solutions, analyzed in detail, and offering a huge range of finned heat exchangers for different industries and applications such as wastewater treatment plants, paper mills, power plants, offshores, chemical industries or food processing plants.

 

Water quality requirements industrial boiler EN12953-10

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EN 12953-10: Water Quality Requirements in Industrial Shell Boilers | BOIXAC Technical blog › Standards & operations EN 12953-10: Water Quality Requirements in Industrial Shell Boilers Technical analysis of the parameters the standard defines for feedwater and boiler water, and their significance for the integrity and safety of steam generation systems. BOIXAC Tech SL Updated: 2026 Reading time: ~10 min Note on the scope of this article This text is intended solely for informational and educational purposes. It does not constitute technical, engineering or water treatment advice, and cannot under any circumstances replace the specific analysis carried out by a qualified specialist on a given installation. The values and parameters mentioned are drawn from EN 12953-10 and the specialist technical literature; they must always be interpreted in the context of the current version of the standard, the boiler manufacturer’s instructions and the requirements of the authorised inspection body. BOIXAC assumes no liability for decisions taken on the basis of the content of this article. Water quality is, alongside design and manufacturing conditions, the single factor that most influences the long-term integrity of a shell boiler. The European standard EN 12953-10 establishes minimum water quality requirements for feedwater and boiler water in this type of equipment, with the fundamental aim of minimising risk to personnel and surrounding installations. For process engineers, maintenance managers and plant operators running steam generation systems, understanding the framework this standard defines — which parameters it controls, why, and according to what criteria — is an essential element of plant technical management. 1. Normative framework and scope The standard EN 12953-10:2003 forms part of the EN 12953 series, which collectively regulates the design, manufacture, documentation and operation of shell boilers (also referred to as firetube boilers). Part 10 deals specifically with the quality requirements for feedwater and boiler water. Its scope covers all shell boilers heated by combustion of one or more fuels or by hot gases, intended for the generation of steam and/or hot water. The standard applies to components between the feedwater inlet and the steam outlet of the generator. The quality of the steam produced is expressly excluded from scope; where specific steam purity requirements apply, additional normative documents are required. Relationship with Spanish operating regulations Spanish Royal Decree 2060/2008 of 12 December, approving the Pressure Equipment Regulations, requires operators of steam or hot water boilers to maintain water within the specifications of UNE-EN 12953-10 (shell boilers) or UNE-EN 12952-12 (water-tube boilers). Compliance is therefore a legal obligation for the installation operator. 2. Technical purpose of the standard: damage mechanisms to be prevented Scale and deposits The precipitation of calcium, magnesium and silicate salts onto heat transfer surfaces creates layers of low thermal conductivity. A deposit as thin as 1 mm can increase fuel consumption by around 5–8 % and locally raise the metal wall temperature to values that compromise its integrity. Corrosion Dissolved oxygen and free carbon dioxide are the primary corrosive agents. Oxygen corrosion produces localised pitting that can progress until the tube wall is perforated. Inadequate pH promotes various forms of chemical attack on carbon steel. Foaming and carry-over The presence of total dissolved solids (TDS) at elevated concentrations, or of certain organic substances, can cause foam formation at the water surface. This leads to carry-over of boiler water droplets into the steam (priming), contaminating the steam with salts. Sludge and blockages Suspended impurities and precipitates not removed by blowdown can accumulate as sludge in low-velocity water zones, impeding circulation and heat transfer, and promoting under-deposit corrosion. 3. Fundamental distinction: feedwater and boiler water The standard precisely distinguishes two types of water that have different requirements and are controlled independently. Feedwater is the water entering the boiler to replace the evaporated volume. It is typically a mixture of recovered condensate and make-up water, having undergone the necessary external pre-treatment processes. Boiler water is the water present inside the boiler drum during operation. Because feedwater is a continuous source of impurities, boiler water undergoes progressive concentration of these substances. Its admissible parameters are managed through system blowdown. 4. Quality parameters: technical description pHat 25 °C Determines the acidic or alkaline character of the water. Moderately alkaline feedwater pH inhibits oxygen corrosion; in boiler water, alkalinity is required to maintain steel passivation. Total hardnessCa + Mg, mmol/l Expresses the concentration of calcium and magnesium ions, the main scale-forming species. The standard requires extremely low levels in feedwater, which in practice necessitate softening or demineralisation treatment. Dissolved oxygenO₂, mg/l Primary corrosive agent. Must be eliminated by combining thermal deaeration with oxygen scavenger dosing. The standard distinguishes limits according to the design pressure of the boiler. Direct conductivityµS/cm at 25 °C Indirect indicator of total dissolved solids (TDS) concentration. The standard classifies the operating regime according to whether feedwater direct conductivity is above or below 30 µS/cm. Acid conductivityµS/cm, after cation exchanger Determined by passing the sample through a strongly acidic cation exchanger. Particularly sensitive to CO₂, chlorides and sulphates, providing a more reliable measure of aggressive anions. Total ironFe, mg/l Originates primarily from corrosion of steel pipework in the condensate circuit. Forms deposits on heating surfaces that degrade heat transfer performance. Total copperCu, mg/l Originates from corrosion of copper-alloy equipment and pipework in the circuit. Its deposition on steel surfaces can accelerate galvanic corrosion. SilicaSiO₂, mg/l Forms calcium and magnesium silicate scale with very low thermal conductivity and high mechanical hardness, difficult to remove without chemical cleaning. Its limit in boiler water varies with operating pressure. Oils and greasesmg/l Their presence causes intense foaming and water carry-over with steam. Can promote corrosion by forming films on metal surfaces that alter heat transfer conditions. Total organic carbon (TOC)mg/l C Organic substances can thermally decompose under boiler operating conditions, generating carbonic acid and other acidic products that raise acid conductivity and cause corrosion. 5. Boiler water parameters: the role of blowdown Because boiler water concentrates progressively, quality management requires an active strategy for impurity removal. The fundamental tool for this is blowdown. The standard provides for the dosing of chemical conditioning agents into boiler water … Read more

HRSG

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Heat Recovery Steam Generator (HRSG): the role of economisers and heat exchangers | BOIXAC Technical guide › Energy recovery › HRSG Heat Recovery Steam Generator (HRSG): the role of economisers and heat exchangers Heat Recovery Steam Generator (HRSG) systems depend on the quality of their heat transfer components. This guide analyses the role of economisers and heat exchangers in optimising these systems, the determining design parameters and the selection criteria for demanding industrial applications. BOIXAC Tech SL Guia tècnica industrial Lectura: ~10 min Table of contents HRSG system fundamentals Definition and application context Thermal architecture and main components The economiser in an HRSG system Function and thermal positioning Key design parameters Heat exchangers: types and integration Quantifiable benefits of thermal integration Component selection criteria In an industrial context where energy efficiency is a determining factor for competitiveness and regulatory compliance, recovering residual heat from exhaust gases represents one of the best cost-benefit interventions available. HRSG (Heat Recovery Steam Generator) systems are the reference solution for this application, and their overall efficiency depends largely on the quality and design of their heat transfer components: in particular, economisers and auxiliary heat exchangers. 1. HRSG system fundamentals 1.1 Definition and application context An HRSG is a thermal recovery system that harnesses the enthalpy of hot exhaust gases from a gas turbine, internal combustion engine or industrial furnace to generate pressurised steam. This steam can be used for electricity generation in combined cycles, industrial heat processes or centralised district heating systems. The main applications of HRSGs include combined cycle gas-steam power plants (CCGT), industrial cogeneration facilities, petrochemical plants and refineries, and processes in the paper, cement and steel industries. 1.2 Thermal architecture and main components A conventional HRSG operates with exhaust gases flowing in counter-current or cross-flow against the water-steam circuit. Energy is transferred successively through several thermal sections, each optimised for a specific temperature range: Gas inlet Hot exhaust gases 400–650 °C at gas turbine outlet. Up to 900 °C in industrial furnaces. Section 1 Superheater Raises saturated steam temperature above the saturation point, preventing condensation in turbines. Section 2 Evaporator Converts liquid water into saturated steam at constant pressure. Phase change zone. Section 3 Economiser Preheats feedwater to near saturation point, extracting residual energy from already-cooled gases. Gas outlet Cooled gases 90–180 °C under optimal conditions. The economiser is key to minimising this value. Note on acid dew point temperature In applications with sulphur-containing fuels, the gas temperature at HRSG outlet cannot be reduced below the acid dew point temperature (typically 120–150 °C for gases containing SO₂), to prevent sulphurous acid condensation on economiser surfaces. This parameter is a critical design limit that directly constrains the maximum achievable energy recovery. 2. The economiser in an HRSG system 2.1 Function and thermal positioning The economiser is a gas-liquid heat exchanger positioned in the low-temperature zone of the HRSG, where exhaust gases have already transferred most of their energy to the evaporator and superheater. Its function is to extract residual enthalpy from these gases to preheat the boiler feedwater. The energy gain is directly proportional to the temperature difference between the water entering and leaving the economiser. A well-designed economiser can raise feedwater temperature from the typical 40–80 °C at deaerator outlet to 180–240 °C, drastically reducing the energy the evaporator must supply to achieve phase change. Industrial boiler economiser. Gas-liquid heat exchanger with helical finned tubes, designed to operate in combustion flue gas streams with inlet temperatures of 250–450 °C. 2.2 Key design parameters Designing an economiser for an HRSG requires the simultaneous analysis of multiple thermal, mechanical and process parameters. The main determining factors are: Parameter Typical range Design impact Gas inlet temperature 200–650 °C Determines material selection and potential corrosion regime Gas outlet temperature 90–200 °C Limited by acid dew point; constrains maximum recovery Water pressure 10–180 bar Defines tube wall thickness and PED requirements Water inlet temperature 40–120 °C Risk of condensation in humid gases; may require recirculation Pinch point temperature 8–20 °C Difference between saturation temperature and gas temperature at same section Gas mass flow rate Process-specific Determines pressure drop on gas side and ID fan power Particle content 0–50 g/Nm³ Determines free passage between fins and cleaning method required 3. Heat exchangers: types and integration Beyond the economiser itself, an HRSG system may incorporate various types of heat exchangers depending on the thermal needs of the associated process. 🔧 Helical finned tubes Preferred type for economisers in combustion gas streams with particulate content. Individual helical fins per tube provide greater mechanical robustness and vibration resistance. Fin pitch can be configured to minimise fouling in loaded gas streams. 📐 Continuous finned tubes Compact alternative for clean or filtered gases. Higher surface density per unit volume than helical fins, but requires particle-free gases to prevent inter-fin blockage. Common in combined-cycle gas turbine applications. ⚙️ Bare multi-tube For applications where the internal fluid is high-pressure steam or water and the external fluid is a gas with high particle loading or corrosive compounds. The absence of fins simplifies external cleaning and reduces blockage risk. 🌡️ Air pre-heaters (APH) In HRSG configurations coupled to burners, preheating combustion air with residual energy from exhaust gases improves burner efficiency and reduces fuel consumption. The gas-gas heat exchanger is the central component of this recovery. Helical finned tube heat exchanger. Standard type for economisers in HRSG systems with combustion gases containing suspended particulates. 4. Quantifiable benefits of thermal integration Incorporating correctly sized economisers and heat exchangers in an HRSG system produces measurable improvements in several operational and environmental indicators. ⚡ Improvement in overall energy efficiency A well-sized economiser can reduce gas outlet temperature by 80–150 °C, equivalent to recovering 3–8% of the total fuel energy burned. In combined-cycle plants, the economiser directly contributes to the overall electrical efficiency of the cycle. 💶 Reduction in fuel consumption Increasing feedwater temperature reduces the energy the evaporator must supply. For every 6 °C increase in feedwater temperature, boiler fuel consumption is reduced by approximately 1% under typical operating … Read more

Types of heat exchangers

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Types of Heat Exchangers: Classification by Construction and Operation | BOIXAC Technical guide › Heat transfer Types of Heat Exchangers: Classification by Construction and Operation Encyclopaedic guide to the main families of heat exchangers: from the distinction between direct and indirect contact to classification by fluid pair. Reference base for engineers, designers and technical managers. BOIXAC Tech SL Referència tècnica enciclopèdica Lectura: ~12 min Table of contents Classification by construction Direct contact Indirect contact Tube heat exchangers Plate heat exchangers Classification by operation Liquid–liquid heat exchangers Liquid–gas heat exchangers Gas–gas heat exchangers Bulk solid heat exchangers Selection criteria and design impact There are many types of heat exchangers and multiple ways to classify them. This article classifies them according to classification by construction and classification by operation, which considers the fluid pairs involved and their physical properties. 1. Classification by construction 1.1 Direct contact In direct contact heat exchangers, the two fluids are completely mixed. Cooling towers are the most representative example. Limitation of direct contact Fluid mixing can cause contaminant transfer between circuits. This makes direct contact unsuitable for most process cooling, energy recovery, gas treatment, food liquid and bulk solid systems where circuit separation is a technical or sanitary requirement. 1.2 Indirect contact In indirect contact heat exchangers, the two fluids remain permanently separated by a physical element — usually a metal plate or tube wall — acting as the heat transfer surface without allowing any mixing. Focusing on the two main families — tubes and plates — a comparison can be drawn as follows. Special case: rotary heat recuperators Rotary heat recuperators are a special case within indirect contact. The two fluids traverse the same space alternately. A slight cross-contamination is theoretically possible, but in industrial practice is considered negligible. Feature Tube heat exchangers Plate heat exchangers Compactness Less compact for the same duty High compactness: maximum surface in minimum volume Transfer coefficient Moderate, depending on tube and fin design High thanks to turbulence induced by corrugations Flow cross-section Wide; less susceptible to fouling Narrow channels; risk of blockage Viscous / loaded fluids Highly recommended. High tolerance to particles and viscosity Unsuitable for dirty, viscous or sticky fluids Maintenance and cleaning Simple. Rarely clog; low maintenance cost More susceptible to scaling; more frequent cleaning required Dusty / abrasive environments Excellent performance Not well suited Preferred application Gas-gas, gas-liquid, liquid-liquid in demanding conditions Liquid-liquid in clean, controlled circuits 1.3 Tube heat exchangers Tube heat exchangers consist of cylindrical, flat or oval tubes, the cross-section being selected according to the specific requirements of each system. 1.3.1 Bare tubes When the internal and external exchange surfaces are similar — fluids with comparable specific heats — bare tubes are used: bare-tube multi-tube exchangers for gas-to-gas, and tubular, multi-tube, shell-and-tube, coaxial or double-pipe, and fire-tube configurations for liquids. Multi-tube heat exchanger. Common in liquid-liquid applications with clean or moderately viscous fluids. 1.3.2 Finned tubes When the two fluids have very different specific heats — a common situation when one fluid is a gas and the other a liquid or steam — the exchange surface must be compensated by adding fins on the side of the fluid with lower specific heat. Why are fins necessary? Quantitative example The specific heat of gas (dry air) is approximately 1.214 kJ/m³·K, while that of water is 4.186 kJ/m³·K. Water can give up or absorb almost 3.5 times more energy per unit volume than air. To compensate for this imbalance, the exchange surface on the gas side is enlarged using fins. Gas (dry air) — 1.214 kJ/m³·K1.214 kJ/m³·KSaturated steam — ~2.010 kJ/m³·K~2.010 kJ/m³·KThermal oil — ~2.000 kJ/m³·K~2.000 kJ/m³·KWater — 4.186 kJ/m³·K4.186 kJ/m³·K Finned tubes Continuous fins (transverse to the tubes) Continuous perforated sheets through which tubes pass perpendicularly. Uniform distribution of fin surface. Common in industrial HVAC and heat recuperators for exhaust gases with relatively clean air. Finned tubes Helical fins (wound around the tubes) Sheets wound helically around each individual tube. Greater mechanical robustness and vibration resistance. Used for combustion gases, industrial fumes and streams with some particle content. Heat recuperator (economiser) for industrial boiler. Gas-liquid application with helical finned tubes. 1.4 Plate heat exchangers Plate heat exchangers consist of flat or corrugated plates acting simultaneously as heat transfer surface and as structural element of the flow channel. Plates Pillow plate heat exchanger Emerging technology of great versatility. The cushion-shaped surface allows working with viscous, sticky and particle-laden fluids, and transferring energy to granular solids as an alternative to fluidised beds. Plates Cross-flow heat exchanger Plate system in perpendicular flow configuration, widely used in HVAC energy recovery. Achieves high efficiency values but requires advanced air filters due to the difficulty of internal cleaning. Welded plate heat exchanger Plates are joined by welding, forming a rigid assembly without gaskets. Internal cleaning is not possible; only applicable with completely clean fluids generating no scaling. Gasketed plate heat exchanger Gaskets allow individual plates to be dismantled, cleaned and replaced. More versatile than the welded type, but channels remain narrow and susceptible to blockage with viscous or particle-laden fluids. 2. Classification by operation Classification by operation considers the fluid pairs involved and their physical properties. Correct selection is essential to maximise efficiency and ensure long-term installation reliability. Liquid–LiquidPillow plate · Welded platesGasketed plates · Concentric tubesCoaxial · Shell-and-tube · Double pipeLiquid–GasBare tubesContinuous finned tubesHelical finned tubesHeat recuperatorsGas–GasMulti-tube · Bare tubesCross-flow · RotaryFlue gas recuperatorsBulk solidsPillow plate(alternative to fluidised beds) 2.1 Liquid–liquid heat exchangers In applications where both fluids are liquids, specific heats are usually similar. Selection depends mainly on fluid viscosity, suspended particle content and operating pressures. 2.2 Liquid–gas heat exchangers This is the situation where the difference in specific heats is most significant. Gas has a much lower specific heat than typical liquids, making it necessary to considerably increase the exchange surface on the gas side using fins. 2.3 Gas–gas heat exchangers When both fluids are gases, their specific heats are similar. However, the low convection coefficient of gas makes it necessary to increase the total surface to … Read more

Coil for temperature control in wine tank

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COIL FOR TEMPERATURE CONTROL IN WINE TANK OPTIMIZATION OF TEMPERATURE CONTROL IN CULTIVATION TANKS One of the largest sparkling wine producers has implemented a temperature control system for 23 cultivation tanks with a total capacity of 142,000 liters, aiming to ensure optimal fermentation and maintain the quality of the final product. This project has focused on processes taking place in the so-called yeast farms, two rooms where fermentation occurs over five days at a strict temperature range of 18 to 20 ºC. Composition and process conditions The fluid present in the tanks consists of wine solution, tirage liqueur (a sugar-rich syrup), and yeast. This combination is essential for fermentation, as the yeast converts the sugars in the liqueur into alcohol and carbon dioxide, producing the characteristic foam of sparkling wine. Maintaining the fluid temperature within the specified range is crucial for ensuring controlled, high-quality fermentation. Heat exchanger system with internal coils To achieve this thermal control, heat exchanger coils have been introduced inside the tanks. These coils, made of AISI 316 stainless steel with electropolishing, provide excellent corrosion resistance and ensure maximum hygiene, two essential factors in sparkling wine production. The coils are certified under the MOCA (Materials in Contact with Food) standard, ensuring the materials used meet food safety requirements. CLAMP no need All system components have been custom-designed to perfectly fit the tanks’ characteristics and the client’s needs. A design eliminating the need for CLAMP connections was chosen, reducing the risk of leaks and simplifying system cleaning and maintenance. This tailored approach has also maximized heat exchange efficiency and optimized temperature control throughout the fermentation process. Wine tank heat exchanger coil benefits Implementing this system has provided numerous operational advantages: Thermal Stability: Maintaining a constant temperature within the specified range has been key to ensuring homogeneous, high-quality fermentation. Energy Efficiency: Electropolished stainless steel coils offer optimal thermal conductivity, reducing the energy consumption needed to maintain the proper temperature. Food Safety: Compliance with MOCA standards ensures the quality and safety of the final product. Reduced Maintenance: The absence of CLAMP connections simplifies maintenance and minimizes potential technical issues. BOIXAC, HEAT EXCHANGE SOLUTIONS This project is an excellent example of innovation applied to the wine industry, where precise control of fermentation conditions makes a significant difference in the quality of the sparkling wine produced. Implementing custom systems and high-quality materials ensures not only process improvement but also greater efficiency and sustainability throughout the production chain. Contact us Heat exchange solutions for the food and beverage industry Water coil Water coil that is often used to condition the environment of greenhouses and breeding farms, improving animal welfare. Energy economizer Energy economizer or heat recovery system that allows the reuse of excess energy, for example, from biomass boilers. Finned heat exchanger Finned tube heat exchanger, a temperature control system that optimizes durability even in environments with certain contamination factors.

Economizer for greenhouses

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ECONOMIZER FOR GREENHOUSES GREENHOUSES AND FARMS An economizer for greenhouses or farms refers to the heat recovery system designed to improve efficiency in an environment where, among other things, crop performance is optimized by controlling temperature, ambient humidity, and CO₂. Within the wide range of implementations, we highlight three main areas: 1. The first block refers to water treatment for the hydroponic growth of tomatoes, lettuces, peppers, strawberries, etc. Hydroponic cultivation allows plants to grow faster and more vigorously thanks to direct access to nutrients. These nutrients are dissolved in a water flow that is distributed to the plants through channels. For proper nutrient absorption, it is important to maintain the water within certain temperature ranges, which is achieved thanks to our finned tubes. This heat exchange system can use spiral fins or continuous fins following the same direction as the tubes, maintaining a homogeneous temperature and optimizing both plant growth and quality. 2. The second block is air treatment through overhead ducts, where BOIXAC provides the finned heat exchangers that condition the air in the greenhouse or breeding farm. These exchangers can include various accessories such as fans, humidity controls, and temperature controls. 3. The third block refers to the technology that enriches the environment, thus increasing photosynthetic activity. We achieve this by reusing the excess energy from exhaust gases through the ECO, AIRY, or GASY heat recovery systems. These thermal exchange units are selected based on primary and secondary fluids; in addition, the materials are also chosen according to the specific needs of each installation. Custom solutions for energy optimization in greenhouses and farms. Heat recovery systems for greenhouses and farms Water coil Water coil that is often used to condition the environment of greenhouses and breeding farms, improving animal welfare. Energy economizer Energy economizer or heat recovery system that allows the reuse of excess energy, for example, from biomass boilers. Finned heat exchanger Finned tube heat exchanger, a temperature control system that optimizes durability even in environments with certain contamination factors.

Industrial economizer

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Industrial economiser: operation, applications and selection criteria | BOIXAC Technical guide › Energy recovery Industrial economiser: operating principle, applications and selection criteria The economiser is the component that converts the residual heat from boiler exhaust gases into a measurable reduction in fuel consumption. This guide analyses its operation, constructive types, main industrial applications and the technical parameters that determine its selection. BOIXAC Tech SLGuia tècnica industrialLectura: ~9 min Table of contents 1. Definition and function of the industrial economiser 2. Operating principle in an industrial boiler 2.1 Energy flow and positioning 2.2 Heated fluids: water, steam and thermal oil 3. Constructive types of economisers 4. Quantified energy and economic benefits 5. Main industrial applications 6. Selection and design parameters In an industrial boiler, between 10% and 20% of the fuel energy burned is lost as sensible heat in the exhaust gases discharged to atmosphere. The economiser is the device that recovers this energy and transfers it to the boiler feedwater, reducing fuel consumption without modifying the main process. 1. Definition and function of the industrial economiser An industrial economiser is a gas-liquid heat exchanger installed at the outlet of combustion gases from an industrial boiler or furnace. Its function is to transfer the residual enthalpy of these gases to the boiler feedwater, preheating it before it enters the boiler body. The term economiser derives directly from its function: to save fuel. By preheating the feedwater, the energy the boiler must supply to reach the vaporisation or working temperature is reduced, translating directly into lower natural gas, diesel or biomass consumption. 10–20%Energy lost in flue gases without economiser3–8%Typical fuel consumption reduction~1%Saving per 6 °C feedwater temperature rise1–3 yearsTypical payback period 2. Operating principle in an industrial boiler 2.1 Energy flow and positioning In a conventional industrial boiler, gases leave the boiler at temperatures typically between 200 °C and 450 °C. The economiser is installed precisely at this point — at the boiler gas outlet and before the stack — to extract residual enthalpy from these gases and transfer it to the feedwater. Gas inlet200–450 °C→EconomiserGas → liquid heat transfer→Gas outlet120–200 °C↕Water inlet40–80 °C→Preheated water130–220 °C to boiler Lower limit: acid dew point temperature The gas temperature at economiser outlet cannot be reduced indefinitely. In sulphur-containing fuels (diesel, heavy fuel oil, some industrial gases), the minimum temperature is set by the acid dew point temperature (typically 120–150 °C), below which condensed sulphurous acid attacks the metal surfaces of the economiser. For clean natural gas, this limit falls to approximately 55–65 °C. 2.2 Heated fluids: water, steam and thermal oil Although the classic function of the economiser is feedwater preheating, in industrial environments the recovered heat can be transferred to other process fluids: Boiler feedwaterClassic application. Water is preheated from the 40–80 °C typical at deaerator outlet to 130–220 °C, reducing the energy the boiler must supply to generate steam.High-pressure superheated waterIn high-temperature circuits for industrial heating processes, the economiser preheats the high-pressure circuit return water.Thermal oilIn thermal fluid boilers (Therminol, Dowtherm, Marlotherm), the economiser preheats the circuit return oil, reducing consumption by 5–12%.Combustion air (APH)In air pre-heater configuration, exhaust gases heat the combustion air before the burner, improving combustion efficiency and reducing NOₓ emissions. Industrial boiler economiser. Gas-liquid heat exchanger with helical finned tubes, designed to operate in combustion flue gases with inlet temperatures of 250–420 °C. 3. Constructive types of economisers The internal construction of the economiser determines its behaviour against combustion gases and its suitability for each application. Main typeHelical finned tubes Each tube carries a sheet metal fin wound helically. The helical geometry provides greater mechanical robustness and resistance to vibrations induced by combustion gas pulsations. The pitch between turns can be adjusted to accommodate particle-laden gases (fly ash, soot). Preferred application: natural gas, diesel, heavy fuel oil, biomass and industrial waste boilers. Environments with suspended particles in the gases. Compact alternativeContinuous finned tubes Flat perforated sheets through which tubes pass perpendicularly. Allow a higher surface density per unit volume, resulting in more compact equipment for the same recovery duty. Require gases without significant particle content to prevent inter-fin blockage. Preferred application: natural gas boilers in clean environments or with prior gas filtration. Installations where dimensional constraints are critical. BOIXAC gas-liquid heat exchangersCustom-designed and manufactured heat recuperators and economisers for industrial boilers, furnaces and combustion processes. View heat recuperators → 4. Quantified energy and economic benefits Installing a correctly sized economiser in an industrial boiler produces measurable and verifiable improvements in the overall performance of the installation. ⚡Reduction in fuel consumption The standard industry rule of thumb states that for every 6 °C rise in feedwater temperature, boiler fuel consumption decreases by approximately 1%. An economiser that raises the temperature by 60 °C can represent savings of 8–10% of fuel costs. 🌿Reduction in CO₂ emissions Lower fuel consumption translates directly into fewer CO₂ and NOₓ emissions per unit of useful energy produced. In facilities subject to emissions trading (EU ETS), the economiser is one of the interventions with the best investment ratio per tonne of CO₂ saved. 🔩Reduced thermal stress on the boiler Preheated feedwater reduces thermal shock at the boiler inlet, decreasing temperature gradients across the shell and tubes. Contributes to extending boiler service life and reducing preventive maintenance frequency. 💶Typical payback of 1 to 3 years In continuously operated industrial boiler installations (>4,000 h/year), return on investment is typically achieved within 12 to 36 months, depending on fuel price, boiler output and the recoverable temperature differential. 5. Main industrial applications The industrial economiser finds application in any process where a boiler or furnace generates residual combustion gases at a temperature sufficient to make heat recovery economically viable. Food and beverage industrySteam boilers for cooking, sterilisation, pasteurisation and drying processes. The economiser preheats the boiler feedwater, reducing energy consumption in the production process.Chemical and pharmaceutical industryThermal fluid boilers for reactors, distillers and dryers. The economiser preheats the circuit return oil, improving cycle efficiency and reducing natural gas consumption.Paper and textile industryLarge steam boilers for continuous drying processes. … Read more