Roots blowers are rotary lobe compressors that generate pressurized or vacuum air for industrial processes. By utilizing positive displacement technology, rotary lobe blowers find use in applications, which require relatively constant air flow rate at varying discharge pressure conditions. These air and gas handling systems have been used for over a century in many industries.
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Design, production and installation of proper equipment for harsh environments and toughest applications requires a great deal of know-how and long years of experience. Polimak manufactures roots type positive displacement blower packages for extensive range of industrial applications. Simple installation, low maintenance need, long years of problem free service, endurance for harsh environments are key features of Polimak blowers. Wide range of roots blower models and accessories are available depending on process parameters and site conditions.
Main components of the blower are two impellers (also referred as rotors or lobes). These impellers rotate in oppposite directions. As they rotate, a fixed quantity of gas at the inlet side is trapped between the impeller and the casing. The rotating impeller pushes the trapped gas to the discharge side against whatever pressure exists in the system. The cycle repeats six times with every revolution.
Rotary positive displacement pump, also referred to as positive displacement (PD) blowers or roots blowers, are machines that 'pushes' a relatively constant volume of gas through a system. Unlike compressors, a roots blower does not internally compress the gas. The compression is achieved through the blower pushing the constant volume against restrictions downstream in a pressure system. Flow through a PD machine is relatively constant, regardless of pressure changes. This is different from a centrifugal compressor, which maintains a relatively constant pressure while the flow varies.
Since blower impellers do not make contact with each other and housing, no lubrication is required in gas conveying chamber. Therefore there exists no extra material in the conveying medium. This feature makes roots blowers have a great advantage in applications that require clean air or gas like aquaculture, milling, pneumatic conveying of foods and, chemicals.
Positive displacement blowers can be delivered as bare shaft units.
For an easy installation option, blowers can be prepared within a package unit which contains electrical motor, silencers and other accessories.
Rotary lobe blower is a positive displacement pump that uses two impellers (rotors or lobes) to displace a fixed quantity of gas. The gas is forced out of the discharge side against whatever pressure exists in the system. This type of pump is often used in industrial applications to move gases that require relatively constant flow rate at varying pressure conditions. The main benefit of using a Roots blower is its ability to maintain high efficiencies over a wide range of flow rates. This makes it an ideal choice for many industrial applications.
'Rotary lobe blowers' , 'rotary lobe compressors' are other names of 'roots blowers' used in industry. The term 'Roots Blower' was named after American inventors and brothers Philander and Francis Marion Roots, who in attempted to improve the efficiency of their water wheel power in Connersville. They patented the basic design in and The Roots Rotary Positive Blower Principle is now well known throughout the world. and still
Twin lobe rotary air blowers belong to category of positive displacement blowers. They consist of a pair of 'lobes' or 'rotors' inside an oval shaped casing, closed at ends by side plates. The two lobes are driven by a pair of precision machined gears which rotate at same speed but in opposite direction. As the rotors rotate, air or gas is drawn into inlet side of the blower housing and forced out the outlet side against system pressure. With each revolution, six such volumes are displaced (in tri-lobe blowers). The air, which is forced out, is almost not allowed to come back due to the small clearances between rotors and casing. Only little amount of air can 'SLIP' back through the clearances.
Positive displacement pumps are called so because of 'no fluid comes back to its casing during pumping out. A locking is formed by lobes or rotors, that acts like a seal and whole amount of fluid goes through delivery line. A positive displacement blower has an expanding cavity on the suction side and a decreasing cavity on discharge side. Gas flows into the expanding cavity at the inlet side and then the same amount of gas is discharged as the cavity reduces at the outlet side. Thus a constant flow is maintained by the pump. This amount is called positively displaced amount and thats why its called positive displacement blower.
As there is no change in volume of the air and there is no compression within the blower, it merely displaces the air from the suction end to the discharge end. The pressure increase occurs at the discharge end against the system resistance. Similarly the increment of cavity at the suction side develops the suction pressure in vacuum applications.
Positive displacement technology enables roots blowers to be used in industrial applications that require relatively constant flow rates at varying pressure conditions.
Compressors, fans, and blowers are widely used in wide range of industrial applications. These devices are quite suitable for complex processes and have become indispensable for today's industry. Generally speaking, fans, blowers and compressors are differentiated by the method used to move the air and by their compression ratio (or in other terms by the system pressure they must operate against).
Classification With Respect to Compression Ratio
Type Compression Ratio Average Operating Pressure * Fan 0 ' 1,3 0 ' 0,25 bar Blower 1,1 ' 2,5 0,15 ' 2 bar Compressor > 2 3 ' 12 bar* Average operating pressure is the pressure range that the system is generally used in today's industrial applications.
With respect to recent developments in gas handling technologies, it is not easy to define a strict pressure range, compression ratio or method of gas pumping for each type of air handling system. i.e. high pressure fans can reach 0,4 bar and they can still be called either as a fan or a blower depending on industrial application, country or sector. Another example is single stage turbo blowers which follow the compression principle of the centrifugal compressors and they are called blowers instead of compressors.
To make a broad definition:
Fans
Fans are used to move large amounts of gas with a low increase in pressure . They are generally used for air circulation in buildings, ventilation, cooling of machniery, dust collection and similar industrial applications.
Blowers
Blowers provide medium amount of gas pressure or vacuum with moderate pressure levels. Blowers are used in processes where the system resistance is higher than that for a fan. They are used in water treatment, pneumatic conveying systems, vacuum applications, industrial processes, superchargers etc.
Compressors
Compressors provide higher pressures by reducing the volume of gases. They are used across the industries to provide shop or instrument air; to power air tools, paint sprayers, and abrasive blast equipment; to phase shift refrigerants for air conditioning and refrigeration; to propel gas through pipelines; etc.
Roots blower application occurs in numerous industries and industrial processes, including pneumatic conveying. Roots blowers play a vital role in many manufacturing and processing systems. Roots blowers are technically referred to as 'positive displacement rotary air blowers' and are commonly known as 'blowers.'
Roots blowers are used to generate constant airflows that are independent of discharge pressure conditions. Root blower applications are limited to low and medium pressure and vacuum processes, and can be used to provide small to large airflow rates.
Roots blowers consist of two identical and symmetrical rotors that have two or three meshing lobes inside an airtight case. The case is valve less and has inlet and outlet ports that are generally on opposite sides. The rotors counter-rotate and are synchronised using a set of gear wheels.
Air is displaced from the inlet to the outlet by the motion of the meshing lobes on the counter-rotating rotors. The rate of airflow from the displacement is governed primarily by the rotational speed of the rotors within the roots blower. There is no change to air volume within the roots blower, so no air compression takes place. Roots blowers are generally air-cooled, and some models operate without the need for oil as a lubricant (oil-free).
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How a roots blower works
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Roots blowers are essential in many bulk material handling and dust collection systems which involve:
They have a wide range of industry applications including:
Raw meal, cement, kiln dust, limestone and coal powder are pneumatic conveyed using roots blowers. They are used to blend raw meal, aerate raw meal and cement and blow air into kilns and burners for combustion. Many cement plants generate their own power using a coal-fired power station. Refer to the power generation section to see how roots blowers are applied in that industry.
Roots blowers are used to transport or compress many inert, corrosive and explosive gases in chemical plants and refineries. These include gases such as nitrogen, hydrogen and chlorine. Also various combinations of hydrocarbon gases. Roots blowers are used in regenerative drying systems to provide ultra-clean and dry air. Bulk dry raw materials, such as aluminium oxide, are pneumatically conveyed, using roots blowers, on gantry ship unloaders and barges. They are used in pressure and vacuum modes in fixed and portable systems.
There are several sectors in the environmental industry where roots blower applications exist.
Roots blowers are used to aerate raw sewage and industrial organic waste. The aeration drives the digestion of the waste by microorganisms. Roots blowers are also used for grit tank cleaning, filter flushing, backwashing and the recovery of gases. Oil-free roots blowers are used for deep cell aeration.
Biogas is referred to as 'digester' or 'landfill' gas. It is made up of methane with small amounts of hydrogen sulphide and other trace gases. Biogas, which is explosive and corrosive, is generated in wastewater treatment plants. Roots blowers are used to transport biogas to where it is burned off or recirculated to fuel combustion engine-driven machines.
Remediation of soil is done when cleaning up accidental spills from vehicles transporting petroleum products and industrial solvents, or leaks from fuel storage tanks. It involves the extraction of volatile organic compounds such as hydrocarbons and solvents. A combination of pressure and vacuum systems is used to evaporate these volatile organic compounds by moving large quantities of air through the contaminated soil. The contaminated air is then processed to remove the hydrocarbons and solvents, and allow safe and immediate exhaust into the atmosphere.
Oil-free roots blowers are used to provide air for ozone production and filter flushing in drinking water purification systems.
Oil-free roots blowers are used to supply air to many food processing and pharmaceutical manufacturing processes. Note that beverages and poultry are included in food processing. Vacuum and pressure pneumatic conveying is used to transfer powder and granular materials such as flour, salt, sugar, grain, spices, chocolate and milk powder for food processing. Dry bulk chemicals are similarly conveyed in the production of many pharmaceuticals. Roots blowers are used to supply vacuum equipment that operates packaging machines. It is common for food and pharmaceutical plants to have large wastewater treatment systems used to decontaminate processed water and treat organic waste. Refer to the environmental section to see how roots blowers are applied in that industry.
Roots blowers are used in marine diesel engine supercharging. They are also used to provide an air supply to bubbler systems on icebreakers and other Arctic duty vessels. They pump inert gas for fuel tank blanketing in tanker ships, and power emergency steering and braking systems on ships. Roots blowers are used to load and unload dry bulk material ships and barges with pneumatic conveying systems. Cruise ships and military craft with large numbers of passengers or crew operating on board have the aeration process within wastewater treatment systems powered by roots blowers. Marinas, locks and harbours use roots blowers to drive air bubbler systems to ensure equipment will operate at sub-zero temperatures.
Roots blowers are extensively used in the mining of most minerals, including copper, nickel, gold and diamonds. They are used to pneumatically convey dry bulk materials and provide air for oxidation processes and other refining applications. Roots blowers are used to filter and dry slurry and power high capacity vacuum pumps. Many mines have large wastewater treatment facilities to allow for the decontamination of processed water - a process requiring roots blowers for aeration.
Roots blowers are used for material handling and pollution control processes throughout the power generation industry. They are used to pneumatic convey fly-ash and lime in both vacuum and pressure modes and are an important part of flue gas desulphurization (oxidation). Roots blowers are used to transfer various bulk dry materials to and from trucks, railway cars, storage silos and hoppers.
Roots blower application occur in many industries and industrial processes
There are many industrial pressure roots blower applications. These range from assisting in combustion by pumping air or gas into burners, furnaces and forges to pressurising paper mill head boxes. The following are some typical examples.
Used in the following industries:
Applied to equipment such as:
Used in the following process:
Used in the following process:
Used in transporting the following materials:
Roots blowers are frequently used as vacuum pumps in dust collecting and drying processes. Industrial vacuum roots blower applications are, however, widespread and include specific industrial processes such as:
Pneuvay Engineering has more than 30 years of industry experience in using roots blowers within pneumatic conveying, vacuum transfer and dust control systems in Australia and around the globe. Contact us online if you need assistance or have some questions regarding roots blowers within these systems.