BOOSTERS FOR MECHANICAL VACUUMS:-
Mechanical vacuum boosters are dry pumps that meet the majority of the requirements for an ideal vacuum pump. They operate on the positive displacement principle and are used to increase the performance of water ring, oil ring, rotating vane, piston, and steam or water ejector pumps. They are used in conjunction with any of the pumps mentioned previously in order to overcome their limitations. Vacuum booster pumps have a number of advantageous properties that make them the most cost effective and energy efficient option.
The primary advantages are as follows:-
(a) Can be used in conjunction with any existing vacuum system, including steam ejectors, water ring pumps, oil sealed pumps, and water ejectors.
(b) The vacuum booster is referred to as a Dry Pump because it operates without the use of any pumping fluid. It is equally adept at pumping vapour or gases. Additionally, small amounts of condensed fluid can be pumped.
(c) Vacuum boosters consume little energy. Frequently, a combination of a vacuum booster and an appropriate backup pump results in a reduction in power consumption per unit of pumping speed. They enable rapid pumping even at low pressures.
(d) Boosters increase the process’s working vacuum, which is often critical for the process’s performance and efficiency. With the proper arrangement of backup pumps, the Vacuum Booster can operate over a wide working pressure range, from 100 Torr to 0.001 Torr (mm of mercury).
(e) Due to the extremely low friction losses of the pump, it requires relatively little power to achieve high volumetric speeds. Typically, their speeds at low vacuum are 20-30 times faster than equivalent vane or ring pumps.
(f) The use of electronic control devices, such as Variable Frequency Control Drives, enables the operating characteristics of vacuum boosters to be modified to meet the operational requirements of the prime vacuum pumps. As a result, they can be easily integrated into any existing pumping configuration to improve performance.
(g) Because vacuum boosters lack valves, rings, and stuffing boxes, they do not require routine maintenance.
(h) Because of the booster’s vapour compression action, the pressure at the booster’s discharge (or backup pump’s inlet) is maintained high, resulting in benefits such as reduced back streaming of prime pump fluid, effective condensation even at higher condenser temperatures, and increased backup pump efficiency.
The table below illustrates how boosters improve process vacuums when used in conjunction with various types of industrial vacuum pumps currently in use in the industry. They are capable of effectively replacing multistage steam ejectors, resulting in significant steam savings and decreased cooling tower load. Mechanical vacuum boosters are adaptable machines whose characteristics are largely determined by the backing pump. Numerous backing pumps are available, depending on the system’s requirements and ultimate vacuum requirements.
However, the final vacuum is determined by the backing pump and booster arrangement chosen. The table below illustrates the range of vacuums that can be obtained using various backing pump combinations.
Vacuum Pump Vacuum that is expected Vacuum during booster installation (single stage)
Ejector Single Stage 150 Torr 15 – 30 Torr 100 Torr Water Ejector Torr Water Ring Pump 10 – 20 Torr 40–60 Liquid Ring Pump Torr 5 – 10 Torr Approximately 20 to 30 Torr Piston Pumps 2 – 5 Torr 20 – 30 2 – 5 Torr
Pumps with Rotary Pistons Rotary Vane Oil Pump 0.1 Torr 0.01 Torr 0.01 – 0.001 Torr 0.001 – 0.0001 Torr.
For instance, if a process employs a water ring pump, the estimated working vacuums would be in the range of approximately 670-710 mmHg gauge (90-50 mmHg abs. ), depending largely on the water temperature and pump design. When a booster is connected in series with the water ring pump, vacuum levels in the range of 5-10 Torr are easily achieved. Vacuum levels of the order of 0.5 Torr & better are easily achievable in a multi-stage booster installation. Unlike steam ejectors, mechanical boosters provide a completely dry pumping solution and do not add to the vapour load, thus eliminating the need for large interstage condenses. At low vacuums, higher pumping speeds are required to maintain the required throughput, as the specific volume increases as the vacuum level decreases. Vacuum boosters increase pumping speeds by approximately three to ten times, depending on the configuration, allowing for increased process rates and throughputs. Mechanical Boosters easily overcome the disadvantages of steam ejector systems, such as sensitivity to motive fluid pressures and discharge pressure, because the volumetric displacements/pumping speeds are insensitive to the inlet and outlet working pressures.
(1) Evaporator (2) Gauge (3) Condenser (4) Mechanical Booster (5) backup Pump
Calculating the Pump Capacity: – Using the fundamental gas laws PV=RT, an expression for the Volumetric Flow Rates required to pump various vapors/gases can be derived. One can estimate the required pump capacity based on the mass flow rates.
V = R Tgas / P Q1/M1 + Q2/M2 Qn/Mn
Where V denotes the flow rate of the Inlet Volume in m3/hr.
Tgas = Gas/Vapor abs. temperature, in oK R = Universal gas constant, 83.14 mbar m3/Kgmol x oK
P = Absolute Pressure in the Process in mbar Q1, Q2, Q3 = Gas / Vapor Flow Rate in Kg/hr
M1, M2, M3 = Molar mass of gas/vapor in kilogrammes per mol.
The operation of the booster is constrained by power constraints, which limit the total differential pressures across the booster. This necessitates maintaining the total differential pressure across the Booster within the rated limits. This can be accomplished in one of the following ways:-
1.) Manual method:- Initially, the fore pump is activated until the desired pressure reduction is achieved, at which point the booster is activated.
2.) Automatic method:- Installation of a mechanical by-pass across the booster, hydro kinematic drive, or variable frequency drive (VFD). The booster and fore pump can be started simultaneously from the atmosphere in this configuration.
The Benefits of Electronic Variable Speed Control
Electronic A.C Variable Frequency Control Drives are the most commonly used devices for regulating the Booster speed to match the process’s varying load conditions. These drives significantly improve the overall performance of the Boosters and provide numerous benefits for trouble-free operation.
The primary advantages are as follows: –
1. The booster is capable of being started directly from the atmosphere.
Everest Transmission January, 2005. Leaders in Vacuum Booster Technology Boosters for Vacuum Processes Everest Transmission January, 2005.
2. No separate pressure switch, bypass line, or offloading valves are required.
3. Significant energy savings.
4. Prevents boosters from overheating.
5. Prevents the Booster from being overloaded or subjected to excessive pressures.
6. Protects the motor completely against overvoltage, undervoltage, overcurrent, overheating, and ground fault.
7. Eliminates the need for a separate motor starter and overload relay.
8. Automatically adjusts the booster’s speed between a low and a high range setting, resulting in high pumping speeds with relatively low input power.
The Electronic Variable Frequency Control Drive is a microprocessor-based electronic drive that has been programmed specifically for the Booster’s requirements, allowing it to operate directly from atmospheric pressure with a suitable fore pump. Boosters are typically started only after achieving a fore vacuum of 30 – 100 Torr, as direct discharge into the atmosphere is not recommended. The use of a pressure switch, hydro kinematic drive, and by-pass valves is required to prevent the booster from overloading. However, with the installation of an Electronic Variable Frequency Control Drive, all conventional methods can be bypassed, as the drive is programmed to automatically regulate the Booster speed, maintaining the motor load within permissible limits. This enables the booster to begin operating concurrently with the backup pump. When the backup pump and booster are started, the drive reduces the Booster speed to pre-set levels, and as the vacuum is created, the Booster speed increases to the final pre-set level, providing the most optimal performance across the entire range. Due to the fact that all parameters are easily programmable, the booster pumping speeds can be easily adjusted to match the system requirements. The drive regulates the motor’s current and protects it from overvoltage, undervoltage, electronic thermal, and overheat ground faults. i.e. guards against all possible faults.
External computer control of all aspects of booster performance is possible via the built-in RS485 serial interface. As a result, the Booster can be integrated into virtually any computer-based operating system.