How tube-in-tube, spiral and plate heat exchangers serve anaerobic digester heating, slurry heat recovery, biogas drying and CHP jacket-water duties in modern biogas facilities.
Short answer
A heat exchanger for biogas applications is chosen per duty, not per plant. Digester heating and feedstock pre-heating handle fibrous, solids-bearing slurry and need open flow paths and mechanical cleaning access, so tube-in-tube, wide-gap plate and spiral constructions dominate. Biogas cooling and drying handle a saturated, H2S-bearing gas that condenses, so material selection, condensate drainage and corrosion control decide the design. CHP heat recovery on jacket water is a clean liquid-to-liquid duty that a plate unit handles well, while exhaust heat recovery is a hot, dirty gas duty for a tubular or finned-tube unit with cleaning access. No single exchanger type covers all four. Bring the flow, temperatures, solids content, gas composition and cleaning method to design review and each duty is confirmed on your data.
Selecting a heat exchanger by biogas duty
Each duty in a biogas plant places a different demand on the exchanger. Use the table to place your duty before comparing constructions, then confirm the selection on measured process data.
| Duty | Governing conditions | Usual construction | Process data required |
|---|---|---|---|
| Digester heating | Fibrous slurry with solids; fouling and blockage risk; low allowable shear | Tube-in-tube, wide-gap plate, spiral | Slurry flow, dry-matter content, viscosity, target digester temperature, heating medium |
| Feedstock pre-heating and pasteurisation | Solids and grit; hygiene or pasteurisation requirement; heat recovery from digestate | Tube-in-tube, spiral, wide-gap plate | Feedstock flow and composition, inlet/outlet temperatures, hold requirement, cleaning regime |
| Biogas cooling and drying | Saturated gas, condensation, H2S and moisture; corrosion at the condensate film | Tubular gas cooler, plate unit in corrosion-resistant alloy | Gas flow, inlet temperature and saturation, H2S concentration, target dew point, condensate drainage |
| CHP jacket-water recovery | Clean liquid-to-liquid duty with close approach and limited space | Gasketed plate heat exchanger | Jacket-water flow and temperatures, heat sink temperatures, allowable pressure drop |
| CHP exhaust heat recovery | Hot, particulate-bearing exhaust; acid dew point; cleaning access | Shell-and-tube or finned-tube gas exchanger | Exhaust mass flow, inlet temperature, target outlet temperature, dust and sulphur content, allowable gas-side pressure drop |
| Digestate heat recovery | Solids and fibres on both sides; fouling on the recovery side | Spiral, tube-in-tube, wide-gap plate | Digestate flow, dry-matter content, temperatures on both sides, cleaning method and interval |
Where heat exchangers fit in a biogas plant
A biogas plant uses heat exchangers in four main locations: digester heating (maintaining 38–42 °C mesophilic or 50–55 °C thermophilic temperature), feedstock pre-heating and pasteurisation, biogas cooling and drying after the digester, and CHP engine jacket water and exhaust heat recovery. Each duty has different fluid, fouling and material requirements.
Digester heating — slurry on one side
Digester content is fibrous, particulate-laden slurry that fouls plate units quickly. Tube-in-tube (double-pipe) and large-channel spiral heat exchangers are the standard choice: open flow paths tolerate solids, allow mechanical cleaning and resist clogging. Hot water from the CHP engine or boiler circulates on the clean side; slurry flows through the open channel on the dirty side.
Slurry-to-slurry heat recovery
Recovering heat from digestate leaving the digester to pre-heat incoming feedstock can cut external heat demand by 30–50%. Spiral or wide-gap plate exchangers in 316L or duplex are the standard solution; the cold and hot slurry streams pass through the unit in counter-flow with sufficient channel width to avoid blockage.
Biogas cooling and drying
Biogas leaves the digester saturated with water and trace H₂S. A water-cooled tube bundle or plate exchanger drops the gas temperature, condenses water for separation and prepares the gas for further treatment (desulphurisation, upgrading). Material selection must account for H₂S — 316L is acceptable for clean biogas; duplex or coated tubes are used where sulphur content is higher.
CHP jacket water and exhaust
The CHP engine that burns the biogas rejects heat through jacket water (~85–95 °C) and exhaust gas (~450–500 °C). Plate heat exchangers recover the jacket-water heat to feed the digester and district heating loops; finned-tube or exhaust-gas economisers recover the higher-grade exhaust heat. Together they convert a large fraction of the engine's input energy into useful process heat.
Materials, hygiene and pasteurisation
Pasteurisation (70 °C for 1 hour) is required in many jurisdictions for animal by-product feedstock. Plate heat exchangers in 316L or 254 SMO handle pasteurisation duties; food-grade gasket compounds (EPDM peroxide-cured) comply with regulations. For acidic digestate or high-chloride feedstock, duplex or titanium constructions are used.
Jiangxing manufactures biogas plant heat exchangers
Shanghai Jiangxing manufactures spiral, wide-gap plate, plate-and-frame and shell-and-tube heat exchangers for biogas plants — digester heating, slurry recovery, biogas cooling, pasteurisation and CHP heat recovery. Send the feedstock, throughput, temperatures and engine size and we will return a selection across all required duties. Blair, blair@shheatex.com, WhatsApp +86 133 1175 6331.
Where to go next
Frequently asked questions
Where are heat exchangers used in a biogas plant?
In four locations: digester heating, feedstock pre-heating and pasteurisation, biogas cooling and drying, and CHP jacket-water and exhaust heat recovery.
What heat exchanger is used for digester slurry?
Tube-in-tube (double-pipe) and large-channel spiral units, because their open flow paths tolerate fibrous, particulate-laden slurry, allow mechanical cleaning and resist clogging.
How much heat can be recovered from digestate?
Recovering heat from digestate to pre-heat incoming feedstock can cut external heat demand by 30–50%, typically using spiral or wide-gap plate exchangers.
Send your working conditions to Blair
Share your medium, temperatures, flow rate and pressure — Blair will return a thermal selection and indicative pricing after reviewing the available data.