I. Features:

During the unit start-up process, when the boiler ignites and the steam turbine is heated, more steam will enter the condenser. If a certain vacuum is not established in the condenser, the steam-water mixture entering will cause the condenser to develop positive pressure, damaging the equipment. Establishing a vacuum in the condenser is an essential condition for the steam turbine to start. In normal operation, the condenser and some low-pressure equipment (such as condensate pumps, blowdown pumps, and some low-pressure heaters) are under vacuum internally. Due to the non-sealed pipes and casings, air can leak in, thereby destroying the condenser vacuum and threatening the safe and economic operation of the steam turbine. At the same time, the partial pressure of air in the condenser increases, causing an increase in the dissolved oxygen content of the condensate, which intensifies corrosion of the thermal equipment and pipelines. The presence of air also increases the heat transfer resistance in the condenser, affecting the cooling of the steam turbine exhaust by the circulating cooling water and increasing the factory's power consumption. Therefore, it is necessary to continuously remove air from the condenser during its operation.

In summary, the function of the vacuum system is: ①Establishing the condenser vacuum during the initial startup of the unit; ②Maintaining the condenser vacuum during normal operation to ensure the safe and economic operation of the unit. The main vacuum equipment for the condenser includes vacuum pumps and ejectors. The water-jet ejector 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 Pump

In modern power plants, the most widely used vacuum pump is the jet vacuum pump, which boasts compact design, simple structure, easy maintenance, reliable operation, and the ability to establish the required vacuum quickly. Jet vacuum pumps are categorized into steam-jet vacuum pumps and water-jet vacuum pumps, based on their working medium. Both types operate on similar principles, differing only in their medium. Steam-jet vacuum pumps use steam under pressure as their medium, while water-jet vacuum pumps use pressure water. Small capacity units predominantly use steam-jet pumps. For high parameter, large capacity units, due to the use of slide parameter start-up methods, there is no possibility of sufficient steam supply for the steam-jet vacuum pumps before the unit starts. Additionally, steam must be throttled from high pressure to 1.2~1.6 MPa for the steam-jet vacuum pumps, which is clearly uneconomical. Moreover, a steam-jet cooler must be installed for recovering the working medium, complicating the thermal system. Therefore, large capacity units in China currently use water-jet vacuum pumps, which are primarily composed of the working water inlet, working nozzle, mixing chamber, diffuser, and check valve.

Water-jet vacuum pump system. It consists of a water-jet vacuum pump, a water-jet pump, a water-jet tank, and connecting pipes. The exhaust from each low-pressure heater, condensate pump, and blow-off pump is collected into a condenser through exhaust pipes, which is connected to the working chamber of the water-jet vacuum pump. Water from a circulating water system or deep well is pressurized by a water-jet pump (one in operation and one as a backup) and then fed into the vacuum pump. The high-speed water jet ejected from the nozzle in the pump generates a high vacuum in the working chamber, extracting the gas-vapor mixture from the condenser. This mixture is then expanded and returned to the water-jet tank.

Section 3: Installation and Precautions for Water Jet Vacuum Pumps

1. Two types of water supply methods for vacuum pumps

The water-jet vacuum pump comes with two water supply methods available for selection.

① Closed-loop system

This is the traditional arrangement, placing the water-jetting vacuum pump above the jet water tank, utilizing the pump—vacuum pump—tank circulation for water supply. 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 system" refers to a射水泵 where the intake is from the recirculation pipe, while the outflow pipe connects to the trench. Its advantages include: a) Reducing water temperature by 4-8°C during summer, which can increase vacuum by 7-15 mmHg; b) The inclusion of a blow-off valve does not affect water temperature; c) It avoids power loss caused by compressing exhaust gases. Its drawback is that it increases the consumption of recirculating water.

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

2. Selection of water intake parameters

Selecting water pumps and motors in accordance with regulations for this series of energy-saving and environmentally friendly water jet vacuum pumps will yield a low-energy, high-efficiency performance. The intake parameters (flow rate, pressure) of the water jet vacuum pump are crucial for enhancing the internal efficiency and reducing energy consumption. This is because the design of the working water nozzle diameter and water pressure determines the velocity at the jet outlet. Moreover, the velocity is related to factors such as the jet angle, throat distance, area ratio, and throat length. Improper matching of the water pump and vacuum pump can affect the operational performance.

3. Installation Precautions

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

①The vacuum pump should be installed vertically, each section should be aligned accurately during assembly, and the support bracket should be firmly fixed.

②The suction pump should be installed at an appropriate height; for suction pumps using closed-loop systems, the remaining speed interface 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 for the outlet pipe is 250-300mm. The supplementary cooling water for the vacuum pump should be added to the pump inlet to maximize its cooling effect.

③For vacuum pumps in closed-loop systems, during summer, it is not advisable to use bottom-mounted vacuum pumps. The structure of the injection 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 before installation, ensuring no leakage for five minutes.

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

⑥ The air intake pipe 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, flange connections are not used to minimize air leakage.