Heat Recovery Of Biogas Generator Unit
1, The core application of waste heat recovery in biogas generator sets
The waste heat of biogas generator sets mainly comes from two parts: the engine exhaust (temperature 350-550 ℃, accounting for 60% -70% of the total waste heat), and the engine cylinder liner and lubricating oil cooling system (temperature 80-120 ℃, accounting for 30% -40% of the total waste heat). Through targeted recycling system design, these waste heat can be widely applied in multiple scenarios, forming a closed-loop ecology of "power generation waste heat utilization":
(1) Ensuring biogas production: raw material pretreatment and fermentation heating
This is the most essential use of waste heat recovery, especially suitable for the stable operation of large-scale biogas projects.
Fermentation tank heating: The optimal temperature for biogas fermentation is medium temperature (30-38 ℃) or high temperature (50-55 ℃). Low temperature environments (winter or northern regions) can lead to a decrease in fermentation efficiency and a sharp reduction in gas production. The recovered waste heat is used to heat the fermentation broth through plate heat exchangers or to provide constant temperature protection for the fermentation tank through a hot water circulation system, increasing gas production by 20% -30% and ensuring stable fuel supply for the winter unit.
• Raw material pretreatment: Some biogas projects use straw, livestock manure, and other raw materials, which need to be heated to achieve decomposition, hydrolysis, or sterilization of the raw materials. The waste heat hot water can be directly used for the raw material pretreatment process, reducing additional energy consumption.
(2) Industrial and Commercial Scenarios: Direct Supply of Thermal Energy
The high-temperature hot water (80-95 ℃) or steam (low-pressure, 0.3-0.6MPa) generated by waste heat recovery can directly meet the thermal energy needs of industrial production and commercial buildings:
Industrial heat: cleaning, drying, and heating processes in industries such as food processing, textile printing and dyeing, chemical pharmaceuticals, etc; Fecal treatment in breeding farms (pasteurization) and constant temperature cultivation in greenhouses (soil heating, air heating).
Commercial and building heating: winter heating for industrial parks, office buildings, hospitals, and schools; Domestic hot water supply for hotels and shopping malls (for washing and kitchen use); Winter insulation for data centers (replacing electric heating).
(3) Energy Upgrade: Waste Heat Power Generation and Refrigeration
For large-scale biogas power generation projects (installed capacity ≥ 1MW), energy upgrading can be achieved through high-end waste heat recovery systems:
• Waste heat power generation: Using organic Rankine cycle (ORC) technology, high-temperature exhaust gas is used to heat organic working fluids (such as R245fa), driving small turbine generators to generate electricity, increasing the overall energy utilization rate of the system to over 80%.
Absorption refrigeration: By using lithium bromide absorption refrigeration units, waste heat is converted into cooling capacity for industrial production cooling and building air conditioning cooling, achieving multi energy complementarity of "summer cooling, winter heating, and year-round water supply".
Waste heat recovery technology not only expands the application boundaries of biogas energy, but also demonstrates multiple advantages in terms of economy, environmental protection, and technology, becoming a "powerful tool" for biogas power generation projects:
(1) Improve the comprehensive utilization rate of energy and reduce energy waste
Traditional biogas power generation projects only focus on electricity output, with a large amount of waste heat directly discharged and an energy utilization rate of less than 45%. Through waste heat recovery, the comprehensive energy utilization rate of the system can be increased to 75% -90%, which is equivalent to more than doubling the effective energy output per cubic meter of biogas. Taking the 1MW biogas generator set as an example, the average daily power generation is about 24000 kilowatt hours, and the recovered waste heat can meet the demand for 20000 square meters of building heating or 500 tons of domestic hot water per day, completely changing the single mode of "only generating electricity, wasting heat".
(2) Reduce operating costs and enhance project profitability
• Reduce fuel consumption: When waste heat is used for heating fermentation tanks, it can replace electric heating and coal-fired/gas-fired boilers, reducing auxiliary energy costs. According to data from a 1.2MW biogas project in northern China, heating the fermentation tank with waste heat during winter can save an average of 300 cubic meters of natural gas consumption per day and save approximately 600000 yuan in annual costs.
• Increase revenue sources: Excess waste heat can be supplied externally (such as heating/hot water to surrounding enterprises and residents), forming a dual income of "electricity+heat", shortening the investment payback period of the project by 1-3 years. The thermal energy revenue of some projects accounts for 30% -40% of the total revenue, significantly enhancing the ability to resist risks.
