I. Features:

During the boiler's startup process and when the steam turbine is warmed up, more steam will enter the condenser. If a certain vacuum is not established in the condenser, the steam-water mixture entering will create positive pressure, damaging the equipment. The establishment of vacuum in the condenser is an indispensable condition for the steam turbine to start up. In normal operation, the condenser and some low-pressure equipment (such as condensate pumps, blow-off pumps, and some low-pressure heaters) are in a vacuum state internally. Due to leaks in the piping and casing, air will infiltrate, thereby disrupting the condenser vacuum and posing a risk to the safe and economic operation of the steam turbine. Additionally, the increase in partial pressure of air in the condenser leads to a higher oxygen content in the condensate, exacerbating corrosion on thermal equipment and pipes. The presence of air also increases the heat transfer resistance in the condenser, affecting the cooling of the turbine exhaust by the circulating cooling water, and increases 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 layout, simple structure, easy maintenance, reliable operation, and the ability to establish the required vacuum in a short 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 typically use steam jet vacuum pumps. For high parameter, large capacity units, since they all use slide parameter startup methods, there is no possibility of having sufficient steam supply for steam jet vacuum pumps before the unit starts. Additionally, steam must be throttled from high pressure steam to 1.2~1.6 MPa for the steam jet vacuum pumps, which is clearly uneconomical. Moreover, a steam jet cooler must be installed to recover the working medium, complicating the thermal system. Therefore, large capacity units in China currently use water jet vacuum pumps, which are mainly composed of a working water inlet, working nozzle, mixing chamber, diffuser, and check valve.

Water Jet Vacuum Pump System. It consists of a water jet vacuum pump, water jet pump, water jet tank, and connecting pipes. The exhaust from each low-pressure heater, the condensate pump, and the blowdown pump are channeled into the condenser through exhaust pipes, which is connected to the water jet vacuum pump's working chamber. Water from the circulating water or deep well is lifted to pressure by the water jet pump (one in operation, one as a spare) and then injected into the water jet vacuum pump. The high-speed water jet emitted by the nozzle in the pump creates a high vacuum in the working chamber to extract 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

There are two types of water supply methods available for the vacuum pump.

Closed-loop system

This is the traditional arrangement, placing the water jet vacuum pump above the water jet tank, with the water 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 tank during summer use.

② Open-loop circulation

"Open-loop circulation" refers to the water intake for the射水泵 coming from the recirculation pipe, with the drain pipe connecting to the trench. Its advantages include: a) During summer, it can reduce water temperature by 4-8°C, which can increase vacuum by 7-15 mmHg; b) The addition of a turboextractor does not affect water temperature; c) It avoids power loss caused by the compression of 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, or entrust our factory to determine it and install the design on behalf of the customer.

2. Selection of Ingress Parameters

Selecting the appropriate water pump and motor for this series of energy-saving and environmentally friendly water jet vacuum pumps ensures low consumption and high efficiency. The intake parameters (flow rate, pressure) of the water jet vacuum pump are crucial for improving 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 exit. The velocity is also related to factors such as the jet angle, throat distance, area ratio, and throat length. Inappropriately matched pumps and vacuum pumps 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, each section should be precisely centered during assembly, and the support brackets should be firmly secured.

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

This energy-saving and environmentally friendly model should not be buried too deep in water due to its relatively lower export speed. Otherwise, it may affect the suction capability 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 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 duct 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 vacuum pump check valve, the height of the air connecting pipe 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. The length should be kept as short as possible to reduce resistance; on the pipeline,法兰 connections are not used except for valves and equipment interfaces, to minimize air leakage.