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Screw expansion engines: excellent helpers for energy savings. 1. Overview: In the production process, there are many situations where steam needs to be depressurized and throttled. For example, the pressure of the steam supplied by the boiler is higher than the pressure required for production; or the pressure of the steam extracted or discharged from a turbine is higher than the pressure needed for production. To ensure production safety and product quality, it is necessary to depressurize and throttle this steam； In industries such as metallurgy, building materials, and ceramics, large amounts of low-grade waste heat are generated during the production process. Companies convert this waste heat into low-pressure steam for use in production or heating, but due to the large volume of heat generated, it often cannot be fully utilized and is instead discharged directly. Screw expansion engines can utilize this waste heat and pressure to convert them into mechanical energy or electrical energy. 2. Appearance of the screw expansion engine 3. Main characteristics of the screw expansion engine · Suitable for various media such as steam, steam-water mixture, hot water, and contaminated heat sources ； ·No need for revving the engine, no disc drive required, no warm-up needed; the unit starts and operates smoothly and easily ； ·It can operate efficiently and safely under conditions of significant fluctuations in heat source parameters ； ·No major repairs for a long time. Simple minor repairs and maintenance ； ·Fully automatic, unattended operation. IV. Main technical parameters of the screw expansion engine: · Steam medium inlet parameters: 0.3～2.5 MPa, 130～300℃ ； ·Internal efficiency of the engine: 65%–80% ； ·Maximum output power: 1500kW ； ·Speed range: 1500–3000 rpm, dynamically adjustable ； ·Dragging loads: generators, various pumps, fans, coal mills, etc. 5 Scope of application: · Industries such as electricity, petrochemicals, chemicals, steel, papermaking, glass, food, and ceramics. 6 Application Examples ★ Using steam pressure differences to drive water pumps, fans, or generators: In industries such as chemicals, papermaking, printing and dyeing, sugar production, and alcohol manufacturing, low-pressure steam at various pressure levels is required (usually between 0.3MPa and 1.0MPa). However, the steam supplied by industrial boilers or power plant boilers has a relatively uniform pressure. To meet the steam needs of all equipment and systems, the pressure of the steam provided is often high; as a result, some equipment requiring steam must use pressure-reducing throttling devices to meet their operational requirements, leading to energy losses and waste. By using a screw expansion engine for pressure reduction and throttling, it is possible to recover the energy lost due to throttling, without any impact on the existing production processes or safety measures. This recovered energy can be used to power generators for electricity generation or to drive industrial loads, resulting in significant economic benefits. Engineering Example 1: Steam from the thermal power plant of a paper mill, with a pressure of 1.0 MPa (gauge pressure), a temperature of 250°C, and a flow rate of 12.5 t/h ； The steam pressure in the papermaking workshop is 0.4 MPa (gauge pressure), with a temperature of 190°C. A screw expansion motor is used for pressure reduction and throttling to drive the 350 kW vacuum pump in the papermill. The screw expansion engine has an output power of 380 kW, saves 2.8 million kWh of electricity per year, and the investment is recovered within 16 months. Engineering Example 2: A chemical plant receives steam from a thermoelectric power plant; the pressure is 0.6 MPa (gauge pressure), the temperature is 230°C, and the flow rate is 15 t/h ； One of the workshops uses a steam pressure of 0.3 MPa (gauge pressure) and a temperature of 180°C; a screw expansion engine is used for pressure reduction and throttling to drive a 300 kW generator, resulting in an annual energy savings of 2.1 million kWh, with the investment recovered within 20 months. Engineering Example 3: A thermal power plant uses an atmospheric deaerator with a pressure of 0.02 MPa. The heating steam comes from the plant’s steam supply main, with a pressure of 0.75 MPa (gauge pressure), a temperature of 260°C, and a flow rate of 4 tons per hour. A screw expansion engine is used for pressure reduction and throttling to drive a 250 kW feed water pump; this setup results in annual energy savings of 1.8 million kWh, with the investment being recovered within 18 months. The table below lists the operating characteristics of various thermal power plant units: 3MW (35t/h boiler), 6MW (65t/h boiler), 12MW (130t/h boiler), 50MW (410t/h boiler). Steam source: turbine extraction steam, turbine extraction steam, backpressure exhaust steam, heating extraction steam. Steam inlet pressure (gauge) in MPa: 0.3, 0.75, 0.98, 1.1. Steam inlet temperature (°C): 200, 260, 310, 250. Exhaust steam pressure (gauge) in MPa: 0.02, 0.05, 0.25, 0.1. Exhaust steam temperature (°C): 106, 111, 186, 120. Steam flow rate (t/h): 3.1, 4.0, 7.7, 22.4. Feed water pump power (Kw): 132, 250, 450, 1600. Feed water pump speed (rpm): 2970, 2980, 2970, 2960. Reduction in plant-specific power consumption: 4.4%, 4.3%, 3.75%, 3.2%. Destination of exhaust steam: deaerator, deaerator, deaerator, low-temperature economizer. ★ Generation of electricity using saturated steam or high-temperature hot water. In small manufacturing plants, low-pressure industrial boilers are often used to supply saturated steam at pressures below 1.3 MPa; however, the steam required for actual production is usually between 0.3 MPa and 0.8 MPa. Therefore, valves are typically used for pressure reduction and throttling to meet the steam requirements for production. Now, screw expansion engines can be used for pressure reduction and throttling, to recover the energy lost during throttling and convert it into power to drive generators for electricity production or to power industrial loads. Engineering Example 1: A factory’s boiler room is equipped with a 10 t/h low-pressure saturated steam boiler, operating at a pressure of 1.25 MPa (gauge pressure). The steam required in the workshops, on the other hand, has a pressure of 0.3 MPa (gauge pressure), a temperature of 160°C, and a flow rate of 8 t/h ； A screw expansion engine is used for pressure reduction and throttling to drive a 350kW generator to produce electricity, resulting in an annual energy savings of 2.5 million kWh; the investment is recovered within 17 months. Engineering Example 2: A power plant utilizes the combined drainage water from three boilers as a heat source for screw expansion engines, which in turn drive generators to produce electricity. These generators have a capacity of 200 kW each; the plant saves 1.4 million kWh of electricity per year, and the investment is recouped within 22 months. The exhaust gas after doing work is then discharged to the series expansion vessel for further expansion. Engineering Example 3: A glass factory generates electricity using the high-temperature flue gas from its production processes. A waste heat boiler is used to produce saturated steam at a pressure of 1.25 MPa (gauge pressure) and with a flow rate of 6 t/h; this steam serves as the heat source for a screw expansion engine, which in turn drives a 400 kW generator to produce electricity. After doing work, the steam enters a condenser where it is condensed into condensate water at around 95°C, which is then sent back to the boiler. Annual power consumption is 2.8 million kWh, with the investment recovered in 14 months (excluding the waste heat boiler). VII. Economic Benefit Analysis Example: A factory uses a screw expansion engine to drive a 400kW electric motor for power generation. The economic benefits are as follows: A. Average annual operating hours: 7200 hours; average electricity price: 0.6/kW·h. B. Annual electricity savings: 400kW × 7200h = 2.88 million kW·h. C. The amount of standard coal equivalent to the heat consumed = 0.16 kg/kW·h (calculated through thermodynamic calculations). D. Annual consumption of standard coal equivalent = 0.16 × 2,880,000 / 1000 = 460.8 tons of standard coal per year. E. If the price of standard coal is 800 yuan per ton, then the cost of power generation = 460.8 × 800 / 10,000 = 368,600 yuan per year. F. Other costs (labor + water consumption): 20,000 yuan per year. G. Economic benefit = 2,880,000 × 0.6 – 368,600 – 20,000 = 1,339,400 yuan per year. VIII. Services and Guarantees: 1. The equipment is guaranteed to have no major maintenance needs for more than five years (boilers are excluded) ； 2. The service life of power generation system equipment is over 20 years ； 3. Annual power generation operating hours > 7200 hours ； 4. The installation adopts a turnkey project approach ； 5. Equipment ordering cycle: 3-6 months (>1000kw systems: 9 months) ； 6. Construction period: 2-4 months.