What Are the Differences Between Screw and Hydraulic Peanut Oil Extraction Machines?

In the field of petroleum processing, screw and hydraulic oil extraction machines, as two kinds of mainstream equipment, show significant differences in core operating principle, oil extraction efficiency and quality, equipment structure and energy consumption, operation maintenance and application scenario. This paper will carry on the thorough comparison from these five aspects, provides technical choice reference for the petroleum processing practitioners.
1.Differences in core Working Principles
Screw Oil Extraction Machines: Dynamic Extrusion and Friction-Generated Heat
Rotating screw is used to propel oil-containing materials to achieve oil oil separation, the pressure chamber space gradually shrinks, resulting in mechanical pressure. What is unique is the friction thermal effect during dynamic extrusion. When oil-containing material is pushed into the chamber by the screw, strong friction will occur between the material embryo, screw and the inner wall of the chamber. This friction not only creates an environment of high pressure extrusion, but also raises the temperature of the oily material to 120-160°C through thermal conversion. High temperature environment will lead to protein thermal denaturation, destroy the colloidal structure, greatly reduce the viscosity of oil, so as to improve oil extraction efficiency. In peanut crushing, for example, the heat generated by friction can boost oil yield by 8 -12% and shorten the crushing cycle to 5-8 minutes per batch.
Hydraulic Oil Extraction Machines: Static Pressure, Low-Temperature Extraction
Hydraulic oil extraction machines adopts high pressure hydraulic system, using hydraulic oil to drive piston to produce linear static pressure. They work in three stages: pre-pressure (pressure up to 10 -20 MPa), primary pressure (pressure up to 40 -60 MPa) and pressure retention (pressure up to 3-5 minutes). Unlike screw equipment, hydraulic pumps produce little mechanical friction heat during stamping, keeping the oily material in the cool range of 50 to 70 degrees Celsius. This low temperature maximizes the retention of thermosensitive nutrients such as vitamin E and sterols in peanut oil, resulting in a decrease of 0.3 -0.5 mg KOH/g for oil and 0.5 -1.0 mmol/kg for peroxide.
2.Comparison of oil recovery efficiency and quality
Oil Yield: Efficiency Advantage of Dynamic Extrusion
oil extraction machines can obtain 42 -48% peanut oil yield by multistage progressive pressing technology. For example, by processing one ton of peanuts per day, screw equipment can produce 420-480 kg of crude oil, 15 -20% more than conventional crushing equipment. Its efficiency stems from three technological breakthroughs:

1. Multi-stage Pressing Structure: 4-6 stage press chamber design, each stage of pressure increase 20 -30%, achieve gradient release of oil.
2. Intelligent temperature control system: using Infrared sensors to monitor the temperature of the chamber in real time, automatically adjust the heating power to ensure that the oily material is in the optimal optimal plastic condition.
3. Mandatory Feeding Device: equipped with frequency converter helical conveyor, solved the problem of clogging ofoil-rich materials, feeding speed increased by 30%.

Although hydraulic oil extraction machines has a pressure of up to 60 MPa at a time, its intermittent mode of operation limits the daily processing capacity to a typical limit of 500 kg. However, its unique segmented pressure holding technology can reduce the residual oil ratio of biscuits to as low as 0.7%, which is irreplaceable in the field of high-end oil extraction. For example, in the production of cold-pressed walnut oil, hydraulic equipment can retain more than 92% of α-linolenic acid, while screw equipment can lose 30 to 40 per cent of this ingredient due to high temperatures.
Oil Quality: The Nutritional Advantage of Low-Temperature Extraction
Peanut oil produced by screw extraction machines needs to be degummed, deacidified, decolorized and deodorized in four refining processes order to meet national oil standards. The content of phospholipids, free fatty acids and other impurities produced by high-temperature pressing is relatively high and needs to be removed by alkali refining deacidification and deacidizing (adding 1% 2% caustic soda solution) and adsorption and decoloration (using active white soil).

1. The cold-pressed peanut oil produced by hydraulic press features a a "natural nutrient repository":
2. Preserve Natural Flavor: Keep 85% or more of the pyrazine volatile substances in peanuts at low temperatures, giving peanut oil a rich nutty flavor.
3. Nutritional Components maintenance: Vitamin E retention rate is 90% per cent and sterol levels are 20 -30% higher than thermobaric oil.

Reduction of Harmful Substances: Benzo pyrene, trans fatty acids and other harmful substances have not been detected and meet the requirements of EU 1881/2006.
3.Differences in equipment structure and energy consumption
Structural design: complexity and Maintenance Costs
Screw oil extraction machines is modular in design and its core components include:

• Power system: equipped with a 3 -15 kW three-phase asynchronous motor, through belt drive speed adjustment.
• Compression system: composed of screw, press chamber and bar cage made of Cr12MoV alloy steel, quenched to HRC58 -62.
• Temperature control system: Integrated electric heating coils and circulating water cooling device to achieve precise temperature control within + -2°C.
• Oil Filtration System: vacuum negative pressure filtration technology, equipped with 304 stainless steel filters, filtration accuracy 5 μm.

Hydraulic oil extraction machines adopts an integrated design, the main components of which include:

• Hydraulic System: composed of high pressure pumping station (up to 60 MPa pressure), hydraulic cylinder and a solenoid directional valve, sealed with aero-grade aluminum alloy.
• Compression system: adopt the whole cast steel press chamber, equipped with adjustable press plate, press gap adjustment range is 0.1-5 mm.
• Control System: equipped with PLC intelligent control unit to achieve automatic control of pressure, temperature and time.
• Safety system: equipped with an overpressure protection device, hydraulic oil leakage alarm device and emergency stop button.

In terms of maintenance costs, screw equipment requires frequent replacement of worn parts such as screws, bar cages, etc. (the annual replacement cost is approximately $2,000-5,000) and hydraulic equipment requires replacement of hydraulic fluid every 2000 hours (the cost is approximately $800-1,500), but there is a high technical threshold for the maintenance of hydraulic components.
Comparison of energy consumption: a trade-off between efficiency and cost
The output energy consumption per unit of screw oil is 8 - 12 kW·h/ton. The main reasons for its high energy consumption are:

• Friction-Generated Heat Loss: About 30% of electricity is converted to heat and consumed.
• Mechanical transmission loss: The efficiency of belt transmission about 92%% and that of gear drive about 95%.
• Continuity Working Characteristics: 24 hours a day is required to maintain productivity.
• The unit output energy consumption of hydraulic pumping units is 15 - 20 kW·h/ton. Although the actual energy consumption per unit of product can be controlled to within 10 - 15 kW·h/ton due to intermittent working. Its energy-saving advantages are as follows:
• Adjustable Pressure Technology: automatically adjust the pressure according to the characteristics of oil-containing materials to avoid ineffective work.

Energy recovery system: Some models are equipped with hydraulic oil cooling recovery devices that can recover 15 -20% of the heat.
Low Standby Power Consumption: off-duty power consumption is only 0.5 -1 kW, which is 80% more energy efficient than screw equipment.
4. Operation, maintenance and Applicable Scenarios
Operational Complexity: Skill Requirements and training costs
The operation of screw extraction machines requires mastery of three core techniques:

• Temperature control: The heating temperature needs to be regulated according to the moisture content of the oily material (when peanuts are 8 -10% water, the optimal pressing temperature is 140-150°C).
• Feeding speed: The feeding rate should be uniform to avoid jamming or idling.
• Residue Cleaning: after each shift, should be cleaned of the accumulation of slag in the ballast tank, to prevent oxidation deterioration affecting the quality of oil.

oil extraction machines pays more attention to process specification:

• Pressure setting: The pressure setting time should depend on the stiffness of the oily material (3-5 minutes for peanuts, 5-8 minutes for walnuts).
• Hydraulic Oil Management: The viscosity (ISO VG46) and moisture content (≤0.1%) of hydraulic oil should be regularly tested.
• Safety protection: Wear protective equipment during use to prevent high pressure oil spray.

Applicable Scenarios: Matching Scale and Demand
Screw oil extraction machines is suitable for the following three situations:

• Production on a large scale: Large and medium-sized oil mills with a processing capacity of 5-20 tons per day can be equipped with automated production lines for continuous production.
• Multi-oilseed Processing: through the replacement of screw, processing peanuts, soybeans, rapeseed and other more than 20 oil-containing materials, equipment utilization is high.
• Thermal pressure process: suitable for the production of strong-scented peanut oil, rapeseed oil and other products that require high-temperature deodorization.

Hydraulic oil extraction machines industry is mainly concentrated in the high-end market:

• Cold pressing process: used for the production of extra-virgin peanut oil, walnut oil and other high-end cooking oil, product value added by 30 -50%.
• Small-batch production: Suitable for small oil mills or home workshops with a processing capacity of 0.5 -2 tons per day, with equipment covering only 10 -15 square metres.
• Special oil extraction: processing flaxseed and grape seed and other high-value oil-containing materials, oil yield than screw equipment screw equipment 8% higher.

V. Technological Development Trends and Selection Suggestions
Currently, two technological lines are converging:

• Intelligentization of Screw Equipment: Fusion with Internet of Things technology to realize remote monitoring, fault diagnosis and production data management. The new screw oil extraction machine, for example, is equipped with an AI stamping model that automatically optimizes process parameters based on the characteristics of oil-bearing material, increasing the oil yield by 2 -3%.
• Efficient development of hydraulic equipment: through high pressure conversion (increasing pressure to 80 -100 MPa) and rapid molding techniques, the pressing time per batch is shortened to 3-5 minutes, with a processing capacity of more than 3 tons per day.
• Composite Processes innovation: a two-stage process of ``screw prepress + hydraulic precision pressure"was developed, in which 70% of oil was extracted by screw machine and the remaining oil was extracted by hydraulic press, with a total yield of more than 52%%.

For small oil mills with an annual processing capacity of less than 500 tons, hydraulic equipment is recommended to ensure oil quality; for large enterprises with an annual processing capacity of more than 1000 tons, screw equipment has a better value for money; and for enterprises producing high-end special oil, composite processing equipment can be considered to achieve a balance of quality and efficiency. With increasing consumer demand for healthy oils, cryo-cooling technology is expected to become the dominant trend in the future, and the market share of hydraulic pumps is expected to increase from the current 25% to more than 40%.