I. Features:

During the boiler and turbine start-up process, when the turbine is warmed up with steam, more steam will enter the condenser. If a certain vacuum is not established within the condenser, the steam-water mixture entering the condenser will create positive pressure, damaging the equipment. Establishing vacuum in the condenser is an essential condition for the turbine to operate. In normal operation, the condenser and some low-pressure equipment (such as condensate pumps, blowdown pumps, and some low-pressure heaters) are in a vacuum state internally. Due to leaks in pipes and casings, air can enter, thus disrupting the condenser's vacuum and compromising the safe and economic operation of the turbine. Additionally, the increased partial pressure of air in the condenser causes an increase in dissolved oxygen in the condensate, which intensifies corrosion on thermal equipment and pipes. The presence of air also increases the thermal resistance in the condenser, affecting the cooling of the turbine exhaust by the circulating cooling water, and increasing the factory's power consumption. Therefore, air must be continuously removed from the condenser during operation.

In summary, the function of the vacuum system is: 1) To establish a condenser vacuum during the initial startup of the unit; 2) To maintain the condenser vacuum during normal operation to ensure safe and economic operation of the unit. The main vacuum equipment for the condenser includes vacuum pumps and steam ejectors. The water-jet vacuum system is widely used in domestic large and medium-sized units due to its simplicity and reliability.

Section II: Structure and Working Principle of Water Jet Vacuum Pumps

In modern power plants, the most widely used vacuum pump is the jet vacuum pump, which boasts compact layout, simple structure, easy maintenance, reliable operation, and the ability to establish the required vacuum in a short period of time. Jet vacuum pumps can be divided into steam jet vacuum pumps and water jet vacuum pumps based on the working medium. Both types of pumps operate on the same principle, differing only in the working medium. The working medium for steam jet vacuum pumps is pressurized steam, while for water jet vacuum pumps, it is pressurized water. Small capacity units generally use steam jet vacuum pumps. For high parameter, large capacity units, since they all use slide parameter startup methods, it is impossible to have sufficient steam supply for steam jet vacuum pumps before the unit starts up. Moreover, steam must be throttled from high pressure steam to 1.2~1.6 MPa pressure for the steam jet vacuum pump, which is clearly uneconomical. Additionally, a steam jet cooler must be installed for working medium recovery, complicating the thermal system. Therefore, large capacity units in China currently use water jet vacuum pumps, which are mainly composed of working water inlet, working nozzle, mixing chamber, expansion tube, and check valve.

Water Jet Vacuum Pump System. It consists of a water jet vacuum pump, a jet pump, a jet water tank, and connecting pipes. The exhaust from each low-pressure heater, condensate pump, and bleed pump are collected through exhaust pipes and fed into the condenser, which is connected to the working chamber of the water jet vacuum pump. Water from the jet water tank, sourced from circulating water or deep wells, is pressurized by the jet pump (one in operation and one as a spare), and then injected into the water jet vacuum pump. The high-speed water stream ejected from the nozzle of the vacuum pump generates a high vacuum in the working chamber, extracting the gas-vapor mixture from the condenser. After expansion, this mixture returns to the jet water tank.

Section 3: Installation and Precautions for Water Jet Vacuum Pumps

1. Two water supply methods for vacuum pumps

The water jet vacuum pump offers two types of water supply methods for selection.

Closed-loop system

This is the traditional arrangement, placing the jet water vacuum pump above the jet water tank, with the jet pump - vacuum pump - tank circulation supplying water. A certain amount of make-up water should be added to control the water temperature in the jet water tank during summer use.

② Open-loop circulation

"Open-loop circulation" refers to the intake of the injection pump coming from the circulating water pipe, while the drainage pipe connects to the trench. Its advantages include: a) It can reduce water temperature by 4~8℃ in summer, which can increase the vacuum by 7~15 mmHg; b) The addition of a residual velocity vacuum pump does not affect the water temperature; c) It avoids power loss caused by the compression of exhaust gases. Its drawback is that it increases the consumption of circulating water.

Before placing an order with our factory, it's best to pre-determine the type of cycle to be used. You may also entrust our factory to determine and install the design for you.

2. Selection of water intake parameters

Choose the water-saving and environmentally friendly jet vacuum pump of this series, and use the specified water pump and motor. This will provide a low-consumption, high-efficiency performance. The intake parameters (flow rate, pressure) of the jet vacuum pump are crucial for improving the internal efficiency of the jet and suction, and reducing power consumption. This is because the diameter of the working water nozzle and the water pressure in the design determine the velocity at the nozzle exit. The velocity is also related to factors such as the jet angle, throat distance, area ratio, and throat length. Inappropriate matching of the water pump and vacuum pump will affect the performance.

3. Installation Precautions

The installation quality of the water-jet vacuum pump is closely related to its suction capacity. Mainly attention should be paid to the following aspects:

①Vacuum pump installation should be vertical, with each section precisely centered during assembly, and the support brackets should be firmly secured.

②The vacuum pump installation height should be appropriate; for vacuum pumps using closed-loop systems, the exhaust port should be more than 1.5 meters above the water surface.

This energy-saving and environmentally friendly model, due to its relatively lower export speed, should not be buried too deep in water. Otherwise, it may affect the suction capacity when the water pressure is low or the water temperature rises in summer. The recommended burial depth of the outlet pipe is 250-300mm. The supplementary cooling water for the vacuum pump should be added to the pump inlet to enhance its cooling effect.

③For vacuum pumps in closed-loop systems, in summer, it is not advisable to use the bottom-mounted vacuum pumps. The structure of the water jet tank should facilitate air exhaust. These measures all contribute to reducing the water temperature in the tank.

④ The vacuum pump body should undergo a hydrostatic test with 0.5 MPa pressure prior to installation, ensuring no leakage for five minutes.

⑤When only one vacuum pump is installed per unit, the air pipe does not need to be excessively high; when two vacuum pumps are installed, to prevent water from flowing back into the condenser through the standby pump's check valve, the air connecting pipe's height should be ≥11 meters.

⑥ The air intake diameter of the vacuum pump is generally the same as the air outlet pipe of the condenser, and the length should be kept as short as possible to reduce resistance; on the pipeline, except for valves and equipment interfaces, flanges are not used to minimize air leakage.