Efficiency is a key parameter when discussing the performance of any industrial equipment including a centrifugal compressor. Although the goal of manufacturers is to keep efficiency values as high as possible, its value varies depending on some factors. In this article, we examine how a typical centrifugal compressor works, its efficiency formula, factors influencing its efficiency, and ways to increase it.

How a Centrifugal Compressor Works

Centrifugal compressors also go by the name dynamic compressors, radial compressors, or impeller compressors. This is because they have an impeller disk that rotates to drive the inflow and outflow of air/gas. The process begins with the rotating impeller sucking air into the compressor via its inlet, which is perpendicular to the disk’s center. 

Inflow of air is encouraged by the curved impeller vanes of the disk, with a volute casing and diffuser vane surrounding the impeller. When air enters the eye of the impeller, impeller vanes and inertia of rotation radially redirect it outwards. The rapidly flowing low pressure air gets forced to the disc’s edge to enter the volute casing through the diffuser. Due to the expanding diameter of the volute casing and the diffuser, the air slows down, thereby increasing the pressure.

In industrial applications, this usually happens in multiple stages to attain the desired pressure.

Compressor Efficiency Formula

Efficiency in centrifugal compressors highlights how effectively they convert input power into kinetic energy, and subsequently into pressure energy. It is commonly expressed as the ratio of the actual work (Wactual) done by the compressor to the theoretical maximum/isentropic work (Wisentropic), as the equation below shows.

    \[ \eta =\frac{W_{actual}}{W_{isentropic}}\times 100% \]

Generally, centrifugal compressors operate within 70 to 90% efficiency, depending on factors like design, operating conditions, and maintenance.

Factors Influencing Efficiency of a Centrifugal Compressor

There are several factors that can affect the efficiency of a centrifugal compressor. The following sections highlight some of them.

Operating Conditions

The efficiency of a centrifugal compressor has a direct correlation with its operating conditions, especially at the inlet. Deviations in parameters such as inlet pressure, temperature, and inlet flow rate can impact efficiency significantly. Take the inlet flow rate for example. Typical performance curves of centrifugal compressors show that as flow rate increases, efficiency also increases. But at one point, the curve reaches the maximum, and there is a decline in performance. This maximum point is referred to as Best Efficiency Point (BEP), which often coincides with the least amount of vibrations in the system. The goal for operators is to always run the compressor at or near the BEP. In addition, filters and other inlet conditioning devices can serve in improving inlet air quality and enhance efficiency.

Design Parameters

The geometric design of compressor features such as impellers, diffusers, volute, and other components, greatly influence efficiency. Analyzing the influence of these features cannot be done separately, rather it entails how the interaction of all component geometries affect airflow through the device. Thus, making this a complex process. However, by using modern computational fluid dynamics (CFD) techniques, manufacturers can optimize geometric parameters of each component and enhance performance.

Another aspect of design parameters that affects compressor efficiency is clearances. Maintaining tight clearances between rotating and stationary components helps minimize internal leakages and improve efficiency.

Mechanical Losses

Like in most mechanical systems, frictional losses within bearings, seals, and other components reduce efficiency. The use of high quality materials, lubrication, and precision manufacturing can help mitigate these losses.

Strategies for Enhancing Centrifugal Compressor Efficiency

To maximize the efficiency of a centrifugal compressor entails improving on any of the conditions mentioned earlier, that influence efficiency values. There are several strategies to achieve this, but the following sections review a few.

The Right Installation

From the onset, getting the installation of the compressor system right is important in maximizing its efficiency. It is necessary to have a proper room ventilation plan and achieve the minimum free spacing for air circulation. Also, air treatment technology should match air quality requirements. On the outlet side, the air piping layout should be such that it minimizes pressure drops, and it must be free of leakages.

Variable Inlet Guide Vanes

In most applications, the demand for compressed air varies from time to time. Having variable inlet vanes helps to minimize compressed airflow at lower load capacity, as well as increase flow at full load. Thus, ensuring that only the required amount of power is utilized per time.

Variable Frequency Drives

Variable frequency drive alters the speed and torque of a compressor by adjusting the frequency of the electricity input. This helps to maintain high efficiency across a wide operating range as demand fluctuates. 

Condition Monitoring and Intelligent Controls

Implementing robust condition monitoring systems enables timely detection of performance deviations, which facilitates proactive maintenance and optimization. In addition, deploying intelligent controls offer quicker response to changing conditions, thereby eliminating dependence on human intervention.

Every project has specific needs, so it is necessary for operators to liaise with suppliers to obtain bespoke solutions. Petrotech’s compressor control solutions provide users with a wide range of flexible and economical compressor control and protection capabilities. By utilizing our multiple algorithms, we can easily install the most cost effective and technically appropriate solution for your compressor application and configuration.

Turbine automation represents a significant leap forward in the operational efficiency, safety, and reliability of power generation systems. By integrating advanced control systems, turbines can operate with minimal human intervention, adapting in real-time to changing conditions to optimize performance. This article delves into the essence of turbine automation and examines the nuanced controls specific to the four principal types of turbines, shedding light on their unique requirements and the technological innovations driving their evolution.  

Turbine Automation

Turbine automation means the use of advanced control systems and computer-aided systems to monitor, control, and optimize the operation of turbines. The goal is to automate the processes that control the turbine’s speed, power output, and other critical operational parameters. Automated systems oversee critical parameters such as temperature, pressure, and flow rate, adjusting operations instantaneously to maintain optimal performance levels. This not only minimizes the need for manual intervention but also significantly improves the turbine’s efficiency and reliability.  By harnessing the power of automation, industries can ensure their turbines operate within optimal parameters, thereby reducing wear and tear and extending the lifespan of these critical assets.

Nuances of Turbine Control Systems

The intricacies of turbine control systems lie in their ability to ensure the seamless operation of turbines under varying conditions. Modern systems embody the convergence of mechanical engineering, electronics, and information technology.

Components of Control Systems

At the heart of turbine automation are several key components, including sensors, actuators, control units, and user interfaces. Sensors constantly measuring parameters such as temperature, pressure, and flow rate. Actuators respond to commands from the control unit, adjust physical components like valves and gates to modulate the turbine’s operation. The control unit, often a sophisticated piece of software running on dedicated hardware, processes sensor data to make real-time decisions. Lastly, the user interface provides a vital link between human operators and the automated system, allowing for monitoring and manual intervention when necessary. The most common deployed user interfaces provide dedicated screens known as HMIs (Human Machine Interfaces). However, modern control systems gradually have seen greater used of non-dedicated control interfaces such as laptops and smart phones that offer the benefit of instant notification to operators.

Functionality and Adaptability

The primary function of turbine control systems is to maintain the turbine’s operation within its optimal parameters, thus maximizing efficiency and longevity. This involves a delicate balance of power output and mechanical stress, requiring a high degree of adaptability. Advanced control algorithms, leveraging techniques from artificial intelligence and machine learning, enable these systems to predict and react to changes in input conditions or demand levels. This minimizes wear and tear while optimizing performance. These algorithms allow for precise control over turbine speed, power output, and other critical operational parameters. They can adapt to changing conditions, ensuring the turbine operates at peak efficiency regardless of external variables. This adaptability is crucial in environments where input conditions (such as steam pressure for steam turbines or wind speed for wind turbines) vary widely.

Integration with Plant-wide Management Systems

Turbine control systems are not isolated entities; they often integrate into broader plant management systems. This integration enables coordinated operation across different plant components, enhancing overall plant efficiency and reliability. For example, in a power generation plant, the turbine control system can synchronize with the grid management system to adjust power output in response to demand fluctuations.

Challenges in Control System Design

Designing effective turbine control systems presents a myriad of challenges. First, the system must be robust, capable of operating reliably in harsh environments or under extreme conditions. This necessitates durable materials and fault-tolerant design principles. Secondly, control systems must be precise. Even minor deviations in parameters can lead to significant efficiency losses or safety hazards. Achieving this precision requires high-quality sensors and actuators, as well as sophisticated software capable of processing complex data in real-time.

Predictive Maintenance and Fault Diagnosis

maintenance on control panel

Incorporating predictive maintenance strategies, turbine control systems can forecast potential mechanical issues before they manifest, significantly reducing unplanned downtime. By analyzing trends and patterns in the data collected from sensors, the system can identify signs of wear and tear or impending failure, prompting proactive maintenance actions. Moreover, advanced diagnostic tools within these systems can pinpoint the source of a problem, facilitating quicker asset repair and reducing maintenance costs.

Evolving Technologies

Advances in technology and shifts in energy demands drive the field of turbine control systems. Emerging trends, such as renewable energy integration and the AI revolution, are shaping the development of next-generation control systems. These systems are expected to be more autonomous, energy-efficient, and capable of integrating with smart grids, marking a significant leap forward in turbine technology.

Ensuring Operational Safety

Above all, the safety of operations is paramount. Turbine control systems incorporate multiple safety features and fail-safes designed to prevent accidents. These systems continuously monitor for conditions that could lead to hazardous situations, such as overheating or excessive pressure build-up, and automatically initiate shutdown procedures if critical thresholds are exceeded.

Compliance with Standards and Regulations

Finally, turbine control systems must comply with national and international standards and regulations governing safety, emissions, and operational performance. Compliance ensures that turbines operate efficiently and adhere to environmental and safety guidelines while minimizing impact on the environment.

Understanding Controls for the Four Main Turbine Types

Each major turbine type presents unique control challenges, necessitating tailored automation solutions.

Steam Turbines

Steam turbines are widely used in power generation and industrial applications. Control systems for steam turbines focus on managing steam flow and pressure to ensure efficient energy conversion. Precise temperature controls are critical to preventing thermal stress and maintaining turbine longevity. Advanced control algorithms adjust the turbine’s operation in response to fluctuating demand and steam supply conditions, ensuring optimal performance under varying loads.

Gas Turbines

Gas turbines, integral to many power plants and aircraft, demand precise control over fuel combustion and air intake. Automation in gas turbines is centered around fuel efficiency and emission control. Real-time monitoring and control ensure the turbine operates within safe temperature and pressure limits, safeguarding against operational risks.

Wind Turbines

Wind turbine controls are designed to maximize energy capture from unpredictable wind resources. This involves adjusting blade pitch and rotor orientation to harness wind energy effectively. Sophisticated sensors and control systems continually adjust the turbine’s settings to optimize performance, contributing to the reliability and efficiency of wind power generation.

PETROTECH’S Solution to Turbine Automation

Petrotech excels in providing cutting-edge turbine automation solutions, tailored to enhance efficiency and reliability across the energy sector. Our state-of-the-art control systems are engineered to optimize the performance of turbines in oil, gas, power generation, and beyond, ensuring superior operational control and energy production optimization. With Petrotech, embrace the future of automated energy with confidence.

Simply put, the decoking process is a procedure for cleaning the tubing and piping of fired furnaces in oil refineries, chemical plants, and other energy supply factories to ensure efficiency, sustainability, and equipment longevity. This process removes the buildup of waste from the production of coke, a fuel made from heating coal without air, and other residues from the tubes.

The Pig Method

A far away shot of a mechanical plant

Many different methods have been used to decoke assets such as furnaces and vessels. These methods including sandblasting, hydroblasting, radiant coils, steam-air decoking, and turbining (which is also used in the control of compressors and generators). However, the pig method is the most popular decoking process in practice today because it can safely and effectively remove coke deposits.

Step One: Prepare the Pipes

Feedstock is a raw product that is transferred through the furnace lines before being transformed into other products or the final product. Before the decoking process can begin, tubing and pipes must be cleaned using steam to rid them of any remaining feedstock, leaving behind only coke residue.

Step Two: Consider the Pigs

The piping is examined to determine its thickness and metallurgical properties. This information is considered when deciding which size and types of pigs to use, as well as the number of pigs that will be needed. Different kinds of pigs are used for different processes; and they vary in shape, size, hardness, and function. The pigs used in decoking fired heaters are called hard-claw or decoking pigs. They remove hard carbon and iron sulfide from furnaces. Other uses include removing calcium scale and cement slurry from pipelines as well as rust and sludge in municipal, industrial, and seawater lines. Each pig has pins that are arranged evenly around its surface, allowing it to scrape off residue without the use of high heat, which can cause corrosion or weaken the integrity of the pipes.

Step Three: Insert the Pigs

Once the pipes are ready and the correct types of pigs have been determined, the next step is to insert the pigs into the furnace tubing. This is done with the use of launchers, which are attached to both the inlet and outlet pipes of the furnace. Once placing is determined, the pigs are forced into the system using air.

Step Four: Push the Pigs Through

Then, using a closed loop system, pressurized water sends the pigs through the furnace tubing and back to the loading point several times to effectively descale the insides of the pipes. Once the debris is completely removed, the pipes are rinsed, and the job is finished.

The pig method efficiently removes coke residue from furnace tubing and maintains the longevity of pipes by using non-damaging materials in an environmentally friendly manner. The volume of water used in the pig method is strictly controlled and is less than conventional methods. Once the buildup inside of the pipes is removed, it flows into a collection tank. In addition to its other benefits, the pig method is approximately five times faster than traditional decoking methods, and there’s no need to disassemble and reassemble piping or use supplementary valves for the pigs.

Custom Decoking Solutions

While the decoking process can be completed in several different ways, the pig method is the optimal choice for cleaning fired heaters. It’s a streamlined process that’s ecologically superior to older methods, effective in the removal of buildup and waste, and gentle on pipes. This process can be easily managed with Petrotech’s decoking control systems, which can be retrofitted for compatibility with existing equipment to maintain productivity. To learn more about how Petrotech can create and install a specialized turnkey system for your facility’s current installations, request a quote today.

steam turbine cutaway

Steam turbines serve as integral components in the petrochemical, power generation, and refinery industries. The foundational architecture of a steam turbine comprises a rotor, precision-supported by bearings and encased within a cylindrical casing. The controlled interaction between steam and meticulously designed blades results in a tangential force and instigates the systematic rotation of the rotor. This intricate arrangement visualizes a steam turbine as a series of windmill-like structures on a single shaft.

Parts of Steam Turbine

steam turbine overview

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.

steam turbine construction diagram

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.

The reversing blade system strategically lies inside the Curtis stage, housing two rows of blades. Acting as conduits, the nozzles embedded in the nozzle ring propel the steam from the steam box to the initial row of blades in the Curtis stage, held securely by the nozzle ring. Once the steam traverses the first row of blades and progresses towards the subsequent blades, the reversing blades help alter the flow direction. The entire unit stabilizes along its length by spacers, reducing vibration and ensuring a smooth-running turbine.

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.

Petrotech’s Steam Turbine Control Support

Petrotech’s advanced steam turbine controls for compressor and generator drive applications feature an integrated control package that provides speed and capacity control. Overspeed protection is implemented in both the software and hardware. To learn more about our line of turbomachinery controls, explore our literature library.