Finned Tube Heat Exchanger for Palm Oil High Temperature Waste Water Waste Gas Waste Heat Recovery

Finned tube heat exchanger for palm oil high temperature waste water waste gas waste heat recovery

Palm oil production will produce high-temperature wastewater (such as cooking wastewater, temperature of about 80-90 ℃) or exhaust gas (such as boiler exhaust), finned tube heat exchanger can be used to recover the waste heat, which will be heated by cold water or air, used for cleaning, heating, or preheating process media, to achieve energy saving and emission reduction.

Waste Heat Recovery of High Temperature Wastewater (Cooking Wastewater)

The temperature of wastewater generated from palm fruit cooking process is usually 80-90℃, which contains a large amount of waste heat (the discharge of wastewater can be dozens to hundreds of tons per hour, depending on the scale of production). If directly discharged, not only waste of energy, but also may lead to environmental thermal pollution. Using finned tube heat exchanger, the heat of wastewater can be transferred to cold water (or other low-temperature media), and the preheated water can be used for:

Palm fruit cleaning (instead of fresh hot water, reducing the heating load of the boiler);

Workshop cleaning, staff living water, etc.;

As a preheated water source for subsequent processes (such as refining link), reducing steam consumption.

Heat exchanger design features

Material selection: as the cooking wastewater may contain a small amount of oil, grease, fruit residue and acidic components, the base tube is mostly made of stainless steel (such as 304 or 316), which is highly corrosion-resistant; the fins can be made of galvanized steel or stainless steel, to avoid rust contamination.

Structural optimization: Fin spacing is appropriately increased (10-15mm) to reduce the risk of clogging of waste water impurities; some designs will be paired with online cleaning devices (such as spray cleaning) to regularly clean the surface of the fins of dirt.

Heat transfer efficiency guarantee: by increasing the fin height (15-25mm) and density, the heat transfer area is enlarged, so that the temperature difference between wastewater and cold water is efficiently reduced from 50-60℃ to 10-20℃, and the recovery rate of waste heat can be more than 60%.

Waste Heat Recovery of Boiler Exhaust Gas

In palm oil production, the temperature of boiler exhaust gas (mostly biomass fuel or heavy oil as energy) is usually 150-250℃, which contains a large amount of sensible heat. Using finned tube heat exchanger to recover this part of the heat, can be heated air or cold water:

heated air as boiler combustion air, increase the furnace temperature, reduce fuel consumption (every 10 ℃ lower exhaust temperature, the boiler thermal efficiency can be increased by about 0.5%);

heated cold water can be used for process preheating (such as palm oil refining preheating before the) or domestic water to reduce the demand for steam.

Heat exchanger design features

Material and corrosion resistance: the exhaust smoke may contain a small amount of sulfur oxides (especially when the fuel contains sulfur), low-temperature section is prone to acid dew-point corrosion, so the finned tube material needs to be acid-resistant steel (such as ND steel) or glass fiber reinforced plastic tubes, the fins are high-frequency welding process to ensure the sealing;

Structure adaptation: the use of air preheaters (finned tubes as the core component), the flue gas goes to the tube course, the air goes to the finned side (lateral flushing fins), fins with the wrong type of fins (the fins), the fins are used in the process. Structural adaptation: air preheater (finned tube core component) is adopted, the flue gas goes through the tube course, the air goes through the fin side (lateral scouring of fins), and the fins are arranged in staggered rows to enhance turbulence and heat exchange efficiency;

anti-dust accumulation design: the spacing of the fins is controlled to be 8-12mm, which reduces the accumulation of smoke and dust; some of the equipment is equipped with dust blowing devices (e.g., steam blowing) to clean up the dust on the surface of the fins on regular basis and to maintain the heat exchange effect in the long-term.

Take medium-sized palm oil mill (daily processing palm fruit 1000 tons) as an example:

Waste heat recovery of cooking wastewater: the heat can be recovered about 5×10⁶kJ per day, which is equivalent to saving about 200kg of standard coal per day, and the annual energy saving benefit is more than 100,000 yuan;

Waste heat recovery of boiler exhaust: if the temperature of the exhaust is lowered from 200℃ to 120℃, it can save about 1 ton of fuel (such as biomass pellets) per day, and the annual saving of fuel cost is more than 300,000 yuan.

At the same time, waste heat recovery reduces the consumption of fresh steam and fuel, indirectly reduces carbon emissions (such as reducing the amount of coal burned in the boiler), conforms to the requirements of environmental protection policies, and is of great significance for palm oil enterprises to realize green production and reduce the pressure of carbon emissions.