Back Pressure Steam Turbine
Dongturbo Electric Company Ltd. (hereinafter call "DTEC") is a professional steam turbine solution provider with ISO and CE certificate, mainly engaged in manufacturing Steam Turbines, Generators, and provide power plant EPC, EPCC and BOT solutions, also supply the equipment Spare Parts, O&M and Retrofitting Service etc.. DTEC is a manufacturing enterprise integrating steam turbine design, manufacturing, installation and service for Power Generation and Industrial Driven Purpose (Pump, Fan etc.) application in the worldwide.
The main products include all types of steam turbines, including condensing steam turbines, back pressure steam turbines, extraction steam turbines, etc. We focus on the development and promotion of single-layer quick-installation and three-station one-stop steam turbines, with high-speed, high-efficiency and energy-saving features, as well as various generators and electrical control equipment matching the steam turbines.
DTEC also can provide customers with one-stop solution for power plant project design, construction, procurement, installation, and commissioning, realizing a true turnkey project, shortening the engineering cycle for customers, and greatly reducing project costs.
Why choose us?
Quality assurance
ISO 9001 certified, Third party inspection available.
Good service
Quick response to customer requirement,Assign special personnel to dock customers.
Reaso nable price
Provide suitable solution according to customer's requirement to save cost.
Fast delivery
Focused on power industry, make reasonable stock ensureour fast delivery.
What is Back Pressure Steam Turbine
Back pressure turbines can either be single-stage or multi-stage which are often used in industrial plants, the turbine serves as a reducing station between the boiler and the process steam header.
The process steam can be produced by back-pressure steam turbines, which also generate mechanical work (or electrical energy). Back-pressure turbines expand the live steam supplied by the boiler to the pressure at which the steam is required for the process. A regulating valve controls the exhaust pressure to suit the needs of the process steam pressure. Back-pressure turbines are commonly found at refineries, district heating units, pulp and paper plants, and desalination facilities where large amounts of low-pressure process steam are needed. The electric power generated by the back-pressure turbine is directly proportional to the amount of process steam required.
Advantages of Back Pressure Steam Turbine
- They can provide mechanical work and reduce steam pressures for the plant process applications.
- They can operate at different RPMs, unlike an electrical motor; thus, they can be directly coupled to a pump, fan, or other device without a reduction gear system.
- Boilers can use different fuels to generate the steam for the steam turbine.
- Backpressure steam turbines can accommodate different steam pressures from very high to low steam pressures.
- Steam temperatures are not a problem and can be dealt with safely.
- Backpressure steam turbines use simple rotary motion, which eliminates the old style of a reciprocating motion and the vibration.
- These turbines extract steam for different steam pressures required by process applications very efficiently.
- They can use superheated or saturated steam for the motive force.
Types of Back Pressure Steam Turbine
Impulse turbine
In an impulse turbine, steam expands through a series of nozzles that direct the steam jets onto the turbine blades. The high-velocity jets of steam impact the blades, causing them to rotate. Impulse turbines are typically used for small-scale applications, such as in power plants with capacities up to a few megawatts.
Reaction turbine
Reaction turbines consist of both fixed blades (stators) and moving blades (rotors). The steam expands as it passes through the fixed and moving blades, and the pressure drops gradually across the stages. This gradual pressure drop allows for continuous expansion of the steam and increased efficiency. Reaction turbines are commonly used in large-scale power plants and can handle high steam flow rates and pressures.
Condensing turbine
A condensing turbine is designed to operate under vacuum conditions. After the steam passes through the turbine, it enters a condenser, where it is condensed back into water. The vacuum in the condenser helps to maximize the pressure drop across the turbine and improve efficiency. Condensing turbines are commonly used in power plants where waste heat recovery is desired.
Extraction turbine
Extraction turbines are designed to extract steam at intermediate pressures for various industrial processes. These turbines have multiple extraction points where steam is tapped from the turbine at specific pressure levels. The extracted steam can be used for heating, feedwater heating, or other industrial processes. Extraction turbines are commonly employed in industries such as pulp and paper, sugar, chemical processing, and district heating.
Reheat turbine
Reheat turbines are often used in large power plants to improve the efficiency of the steam cycle. In a reheat turbine, steam is expanded through the high-pressure section, then reheated and expanded further through the low-pressure section. Reheating the steam helps to maintain its high energy level as it expands, resulting in improved overall efficiency.
Power generation
One of the main applications of back pressure steam turbines is in power generation. In a power plant, the back pressure turbine is connected to a generator that converts the mechanical energy produced by the turbine into electrical energy. The steam used to power the turbine is usually produced by a boiler that is fueled by coal, natural gas, or other sources of energy.
Industrial processes
Another application of back pressure steam turbines is in industrial processes that require high-temperature steam. For example, the food processing industry often uses steam to sterilize equipment and containers. By using a back pressure turbine, the steam produced during the process can be used to generate electricity or drive machinery while also providing the necessary steam for the sterilization process.
District heating
District heating systems use hot water or steam to provide heat to buildings and other facilities within a community. Back pressure steam turbines can be used in district heating systems to generate electricity while also producing the steam needed for the heating system. This can be particularly useful in areas where there is a high demand for electricity and heating.
Waste heat recovery
Back pressure steam turbines can also be used in waste heat recovery systems. In many industrial processes, a significant amount of heat is produced as a byproduct. This heat can be captured and used to produce steam, which can then be used to generate electricity or drive machinery. By using a back pressure turbine, the steam can be used to generate electricity while also providing the necessary pressure for the process.
Components of Back Pressure Steam Turbine
Steam chest and the casing
The steam chest connects to the high-pressure steam supply line while the low-pressure steam exhaust line affixes to the casing as shown in Figure 1. The steam chest positions between the casing houses the governor valve and the overspeed trip valve. The nozzles, located inside the casing, direct the flow of steam onto the rotating buckets.
Rotor
The rotor consists of a bucket-equipped shaft and disc sections. The shaft emerges from the casing and through the bearing cases. A driven pump connects to one end of the shaft and the speed governor and overspeed trip system are located on the opposite end.
The bearing cases
As shown in Figure 1, the bearing cases support the rotor, along with the assembly steam chest and steam chest. The bearing cases contain journal bearings and rotating oil seals. The oil seals keep oil inside and water, dust, and steam out. The steam end bearing case also includes the rotor positioning bearing and the rotating parts of the overspeed trip system. The steam end-bearing case covers the moving parts.
Casing sealing glands
A seal exists between the casing and the shaft provided by the casing sealing glands. For this, the system uses spring-backed, segmented carbon rings. These rings are supplemented by adding a spring-backed labyrinth section that makes the exhaust steam work better.
Governor system
Control systems, called governor systems are built into steam turbines and can sense when the speed changes. They can change turbine speed by changing the governor valve, which controls the steam flow through the turbine. The governor also contains rotating weights that push against each other by a servo motor system. The governor determines the turbine shaft’s speed via a straight link, or a magnetic impulse from a gear. A set point compares the rotor speed and the servo motor receives the governor output signal. Changes in the input and exit steam of the turbine, as well as changes in how much power the pump needs, will dictate the turbine’s speed. When the speed changes, the governor weights move, which moves the governor valve.
Over-speed trip system
The governor takes control of the rotating system, swiftly sealing the trip aperture to interrupt the flow of steam to the engine upon detecting an excessive speed. This arrangement comprises of a turbine shaft collar featuring a pin or weight under spring tension, an expeditious closure valve distinct from the governor valve, and an interconnecting linkage. As the pin rotates within the turbine shaft, it generates a centrifugal force surpassing the spring’s opposition at a specific velocity.
Labyrinth seal
A labyrinth is a structure that is meant to keep fluid from going from a high-pressure zone to a low-pressure zone by letting only a small amount of fluid leak out. Maintaining the smallest possible clearance between the labyrinth and the shaft is important.
Nozzle ring and curtis stage
- Assembly of the nozzle ring and reversing blade in the steam end casing is a meticulous process. The nozzle ring firmly secures to the lower section of the steam end casing through bolts.
- The nozzle ring interfaces with what is called a Curtis stage. This Curtis stage provides an essential part of the turbine’s design, especially in turbines with a significant drop in steam pressure.
- A Curtis stage typically consists of one or two sets of highly specialized blades that typically undergo a specialized heat-treating process to directionally align the grains. After the blades, exists a set of stationary nozzles or guide vanes. The high-pressure steam first passes through the stationary nozzles, where it expands rapidly, converting the thermal energy of the steam into kinetic energy. This high-velocity steam then strikes the moving blades, imparting momentum and thus rotating the turbine shaft.
Sentinel valve
This part is at the top of the exhaust end of the turbine casing and acts as a warning system. It activates when the pressure inside the turbine’s exhaust end casing becomes too high. When the pressure inside the casing rises above a certain level and exceeds the standard working pressure, the valve will release a small quantity of steam that can be seen and heard.
Auxiliary steam valves
Auxiliary valves improve working efficiency when there are changes in load or steam conditions. The valves are inside the steam tunnel, between the steam chest and the nozzle ring at the lower end of the turbine casing’s steam end. The tube splits into three separate sections. One section stays open all the time so that steam can keep going to a bank of nozzles in the nozzle ring. The other two sections contain auxiliary hand valves to control steam flow to two other banks of nozzles within the same nozzle ring.
Turning gears
Large turbines come with gears that rotate to make it easier for the rotors to turn slowly while they warm up and cool down. To keep the shaft or rotor straight and balanced, this is done to ensure consistent temperature around its entire diameter.
Carbon ring seals
The structure is made up of pieces of a carbon ring that are held together by a spring. The anti-rotation stops fit firmly into the notches in the bottom half of the interstage casing. In addition, the carbon rings are used to successfully stop any rotation from happening.
Turbine cylinders
Turbine cylinders have to withstand the pressure of the steam, so they need to be built solidly with thick walls. Because they are exposed to high steam temperatures, thick-walled components are not desirable. When temperature differences exist inside stiff parts, they put a lot of stress on the material. These stresses can break down materials when-added to the mechanical stress that comes from pressure.
How to Maintain Back Pressure Steam Turbine
Maintenance of back-pressure steam turbines is a crucial aspect of ensuring their longevity and optimal performance. Steam turbines are widely used in various industries, including power generation and manufacturing, where they play a key role in generating electricity and providing process heat. To maximize the efficiency and reliability of these turbines, regular and proper maintenance is essential.
One primary aspect of the maintenance of back-pressure steam turbines is the inspection and cleaning of critical components. Over time, deposits and contaminants can accumulate on the turbine blades and nozzles, reducing its efficiency. Routine inspections and cleaning help prevent these issues and ensure that the turbine operates at its peak efficiency.
Another critical element of the maintenance of back-pressure steam turbines involves monitoring and maintaining the lubrication system. Proper lubrication is vital to reduce wear and friction within the turbine’s moving parts, ultimately prolonging its lifespan. Routine checks and oil changes are necessary to prevent any potential damage and ensure that the turbine operates smoothly.
Regular alignment and balancing are also essential in the maintenance of back-pressure steam turbines. Misalignment or imbalance can lead to increased vibrations, which can ultimately cause damage to the turbine and related equipment. Routine checks and adjustments can help avoid these problems.
Finally, safety checks and adherence to maintenance schedules are imperative for the maintenance of back-pressure steam turbines. Ensuring that maintenance is conducted as per manufacturer’s recommendations and industry standards is crucial for preventing accidents and ensuring the longevity and reliability of these critical assets. Properly maintained back-pressure steam turbines not only reduce operational costs but also contribute to overall energy efficiency and sustainability, making them a key component in various industries’ energy infrastructure.
First, the heat energy of the steam (Btu/lb.) is converted into kinetic energy (velocity) by expanding the steam isentropically from a higher pressure to a lower pressure through a nozzle. Steam emerges from the nozzle at a high velocity.
Second, the velocity of the steam is converted into mechanical work by directing the steam against the blades mounted on a turning rotor. A “stage” typically consists of one set of stationary nozzles and one or more rows of rotating blades immediately downstream of the nozzles.
Steam turbines are designed to meet a wide array of applications and performance specifications. Steam turbines for a large utility operation may be designed with several pressure casings and complex design types that maximize the efficiency of the steam thermal cycle in the power plant. In industrial process applications, steam turbines are generally smaller and operate at a lower steam pressure; therefore, the design is less complicated for reliability and cost reasons.
The backpressure turbine design allows the plant to capture mechanical work while providing a very effective way of reducing steam pressures for different process requirements.
Steam turbines capture the mechanical work ability of steam, and they extract steam at different stages to supply different pressures to the processes in the plant. Since the exhausted steam is also used for process applications, the thermal efficiency of a steam turbine system is very high. Boilers can burn different fuels such as black liquor, wood waste, sawdust, fuel oil, coal, methane, etc. This provides great flexibility when using a steam turbine in a plant operation.
Our Factory
The main parts and key components of the products have all realized CNC machining, including Japanese Mitsubishi five-axis gantry machining center, Italian tower base horizontal rotor groove milling machine, 10-meter CNC heavy-duty horizontal lathe, 8-meter CNC vertical lathe, etc., with high precision, strong reliability and advanced processing technology And other characteristics, to achieve the standardization and modularization of product components, and improve the versatility and interchangeability of product components.
