Deaerator working principle, Types and Process Control

Deaerator working principle, Types and Process Control

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Deaerators is commonly employed in any chemical process industry or in Power Plants wherever boiler is utilized for steam production from boiler feed water. Deaerator solves the aim of removal of unwanted dissolved gases and dissolved oxygen from the boiler feed water before going in boilers. Most of the deaerators are designed in such how that the dissolved oxygen content within the outlet water is regarding7 ppb by WTC.

Principle of Dearators

Dearator commonly works based on the subsequent principles.

Henry’s Law

According to Henry’s low is in a liquid the gas solubility is directly proportional to the partial pressure. thus if we tend to decrease the partial pressure of the dissolved gas by adding steam in Deaerator, its solubility decreases and also the gas is faraway from water.

Inverse Solubility of Water

When the temperature of water is growing, the dissolved oxygen content within the water is decreases. Thus the water temp. is growing by inserting steam in Deaerator, the dissolved gas solubility is reduced and also the gases are withdrawal from water.

Types of Deaerators

1. Tray types Deaerator

Tray type deaerators contain perforated trays within the top of the Deaeration section. The bottom portion volume is high for used as storage for boiler feed water. Feed water to deaerator enters into the perforated trays wherever the area and residence time is growing to contact with steam. Then the water goes to the horizontal storage section wherever steam is pass through sparger pipe to withdrawn the remaining traces of dissolved gases and keep the stored water at its saturation temperature.

Tray Deaerator

2. Spray type Deaerator

Spray Deaerator type deaerator contains spray nozzle in feed water entry space. it’s then preheated and deaerated and sent to storage section. In storage section also steam is additional to stay the water at its saturation temperature.

Spray type Deaerator

Process control system in Deaerator

Deaerator operate in very low pressure steam about 0.5 to 1.5 kg/cm2 with can produce in process plant.The low steam sources could also be anyone of the following: Extraction from back pressure turbines, Flash steam recovered from Boiler blow down or letdown steam from high pressure steam header through pressure reducing valve. Steam pressure within the deaerator should be maintained to facilitate the removal of dissolved gases from water and also to produce adequate NPSH to boiler feed pump. Deaerators are commonly put in at high elevation so as to produce enough NPSH within the event of failure in steam pressure control conjointly. Pressure safety valve is additionally fitted to avoid pressurization of deaerator because of malfunctioning of pressure control valve.

Process control system in Deaerator

Water Level control

Main sources of raw water to deaerator are Treated water from water treatment plant and steam condensate from the condensing type turbines. During the stable plant operation the water balance is maintained and through any upset within the higher than said sources water level fluctuates and control is important. High level and low level alarms are provided. Low level might lead to starvation of feed water in pump and High level leads to water entry into steam header. Thus overflow drain is put in to drain the water if very high level is reached.

 

Deaerator Water Level control

 

Other benefits of Deaerator

Dearator acts as an extra storage that provides reserve amount of boiler feed water throughout upstream water supply failure for momentary periods commonly for about twenty minutes.

In some of the Plants, Deaerator is additionally used for dosing oxygen scavenging chemicals like hydrazine or Hydroquinone.

What is a Boiler? & its types

 

Boiler overview

What is a Boiler? & its types

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What is Boiler:- A boiler is outlined as “A closed vessel during which water or different liquid is heated, steam or vapor is generated, steam is super heated, or any combination therefrom, besieged or vacuum, to be used external to itself, by the direct application of energy from the combustion of fuels, from electricity or energy ”.

A Brief Introduction :

Boiler may be a main operating element of thermal power plants.

Water is helpful and low-cost medium for transferring heat to a method.

once water is warm into steam its volume will increase regarding 1,600 times, manufacturing a force that’s virtually as explosive as bomb.

This causes the boiler to be extra ordinarily dangerous instruments and equipment will be treated carefully

Liquid once heated to the vaporous state this method is named evaporation.

The heating surface is any a part of the boiler; hot gases of combustion square measure on one facet and water on the opposite. Any a part of the boiler metal that truly contributes to creating steam is heating surface.

the quantity of heating surface of a boiler is expressed in sq. meters.

The larger the heating surface a boiler has, the a lot of economical it becomes.

 

CPP Boiler Plant over view

Fuel Used in Boiler

The list of major fuels that square measure used in boiler systems is given below:

1. N.G. (Natural Gas)

2. Propane

3. Oil

4. Electricity

5. Solids Fuels like Coal & Wood

6. Renewable Energy

Solid Boiler fuels:- Major solid fuels used for burning in a very boiler embody coal and wood. They were the sole fuel sources obtainable to be used in boiler systems before the emergence of heating heating oil. These square measure the most affordable means that of boiler fuels that are becoming exhausted day by day because uncontrolled use.

• Wood
• Coal
• Briquettes
• Pet Coke
• Rice Husk

Liquid Boiler Fuels :

• L.D.O.
• F.O.
• LPG :- In observe, LPG is especially employed in applications wherever the supply of gas is either terribly restricted or expensive. LPG works as a boiler fuel in similar manner as gas. However, the boiler in use should be capable of conversion options so it may be created compatible with LPG.

Major vaporous Boiler Fuels square measure as :

• LPG
• LNG
• PNG are often accustomed do the combustion for the precise purpose.

Components of Boiler System

There square measure three backbone parts of any boiler system:

1. Boiler Feed Water System

Water that converts into steam by vessel system known as Feed water & system that regulates feed water known as Feed water system.

There square measure 2 styles of feed water systems in boilers:

 

Boiler Feed Water Pump Design

• Open feed System
• Closed feed system

There square measure2 main sources of feed water:

• Condensed steam came from the processes
• Raw water organized from outside the boiler plant processes ( Called: Makeup Water)
• Boiler feed pump: Ring-section model with sound stage
• Multi Stage Boiler Feed pump

2. Boiler Steam System

Steam System is quite main dominant system of boiler method. Steam Systems square measure accountable to gather all generated steam within the method.

Steam systems send steam generated within the method to the purpose of use through pipes ( piping system). Throughout the method, steam pressure is controlled and controlled with the assistance of boiler system components like valves, steam pressure gauges etc.

 Process Flow Diagram

There square measure three backbone parts of any boiler system:

1. Boiler Feed Water System

Water that converts into steam by vessel system known as Feed water & system that regulates feed water known as Feed water system.

There square measure 2 styles of feed water systems in boilers:

• Open feed System
• Closed feed system

There square measure2 main sources of feed water:

• Condensed steam came from the processes
• Raw water organized from outside the boiler plant processes (Called: Makeup Water)
• Boiler feed pump: Ring-section model with sound stage
• Multi Stage Boiler Feed pump

2. Boiler Steam System

Steam System is quite main dominant system of boiler method. Steam Systems square measure accountable to gather all generated steam within the method.

Steam systems send steam generated within the method to the purpose of use through pipes ( piping system). Throughout the method, steam pressure is controlled and controlled with the assistance of boiler system components like valves, steam pressure gauges etc.

3. Boiler equipment

Fueling is that the heart of boiler method consists of all needed|the mandatory} parts and instrumentation to feed fuel to get required heat. The instrumentation needed within the equipment depends on the sort of fuel employed in the system.

Boiler Applications

The Boilers have a really a large application in numerous industries like

1. Food Plant

Food should usually be heated or boiled through out process. so this industrial sector clearly desires lots of thermal energy. However, some steam applications square measure still stunning; a decent example is potato process.

2. Breweries

Most people apprehend that a decent and attractive Breweries consists of hops, malt and water. However, before enjoying the Breweries there’s a posh production method. Malt must be ground coarsely and mixed with water. The brewer calls this mashing. The mash should be heated to numerous temperatures in 2 to four hours. Steam generated with the vessel is generally used as a heat carrier. after, hops square measure else and also the mixture must relax. Then yeast is else and triggers the fermentation so the Breweries gets the specified result. once more when bottles or barrels are empty they’re unremarkable came to the still. in fact the breweries initial got to clean them before they’ll be refilled. For this method steam is once more needed to heat up the water required for cleanup.

3. Building materials Plant

Large amounts of steam also are necessary for the assembly of formed bricks. the fundamental materials like sand, lime, water, etc. square measure mixed and ironed to comparatively loose stone compounds. after, the stones square measure transported to an enormous pressure vessel (autoclave) that is then closed and steam is injected. The stones got to harden at a temperature of roughly two hundred °C and a pressure of regarding sixteen bar for a particular amount of your time and may then be withdrawn as finished stones.

4. Sewer pipe rehabilitation

What to try and do if there’s a drain leakage? This draw back will either be solved by means that of excavation works at the underground pipes and renewal of the waste product pipe systems or with rehabilitation tubes. These tubes square measure over dimension hoses that square measure inserted within the pipes while not excavation work so inflated with steam. The plastic hose attaches itself to the waste product pipe below application of pressure and temperature and also the pipe will still be used for several years.

Many different Industries uses of type boiler like :

• Power Sector
• Textiles
• Plywood
• Food process Plant
• F.M.C.G.
• Sugar Plants, etc

Vacuum Distillation | Vacuum Distillation Process

 Vacuum Distillation | Vacuum Distillation Process

Vacuum Distillation | Vacuum Distillation Process

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Introduction:

Water is available in basically every industrial process; it isn’t just utilized for manufacturing products, but additionally for different purposes accompanying the production process. Water is essential and fundamental in the production of practically any product, whether it is a vehicle or a toothpick. A vast amount of water is spent on the production of paper, food, and synthetic substances. This alleged industrial water generated in production processes is normally contaminated after the production process and polluted with heavy or weighty metals, oils, or salts among different substances of concern.

The contaminated water can cause extreme ecological damage assuming that it is returned to the public supply without being purified ahead of time. Subsequently, an efficient long-haul strategy is to purify or purge the contaminated water directly in the facility where it was produced since the contamination generally makes up just a small fraction of around 2-3% of the wastewater and the purified water can be reused directly in the facility too.

What is Vacuum distillation?

The wastewater is evaporated, the dirt stays behind, and the rising steam is liberated from impurities. The condensate, additionally called distillate, can be reused in production. Along these lines, 100 % wastewater produces around 98 % cleag and water and just 2 % residue, which can be disposed of at minimal expense. The underlying physical principle is named the Distillation of substances as per boiling point differences. Vacuum Distillation is a procedure or strategy of separating a blend of compounds at a pressure that is lower than the normal atmospheric pressure. By reducing their boiling point fully backed up by a vacuum. It is used in the different processes, for instance in Beverage and food production to extract plant substances or to separate long-chain hydrocarbons in Petroleum treatment facilities.

The vacuum distillation method additionally saves energy, since water evaporates under a vacuum at 80 degrees Celsius rather than 100 degrees Celsius. This significantly affects how much energy is consumed. In view of the utilization of heat exchangers as well as the reuse of the evaporation heat in the system, the set-up of a vacuum distillation consumes comparably small electricity. A vacuum distillation plant is suitable for the purpose that is exceptionally energy-saving in contrast to atmospheric evaporation.

How does vacuum distillation work?

In the vacuum distillation process, the industrial wastewater is taken care of into a heat exchanger and evaporated under vacuum. The heat exchanger comprises a bundle of tubes where the wastewater is divided into more modest volumes to make it easier to evaporate. The applied vacuum led then to a modification of the boiling over. This permits water to evaporate at around 185 degrees Fahrenheit (85 °C) rather than 212 degrees Fahrenheit (100 °C) under atmospheric pressure.

All substances with a higher boiling over than water remain in the evaporation residue. The resulting vapor is then taken care of in the vapor compressor. It creates compression heat, which warms up the steam to 248 degrees Fahrenheit (120 °C). From the vapor compressor, the compressed steam raises a ruckus around the tube bundle again where the cooler wastewater is taken care of, Condensing on the outer wall of the tubes. Subsequently, the steam returns to liquid clean water and can be released from the system or returned to the production process. The contaminated evaporation residue is then drained or depleted.

Pre–and after-treatment in the vacuum distillation process:

The heart or core of the wastewater treatment system is the vacuum distillation unit. Contingent upon the nature of the wastewater contamination, pre-treatment and post-treatment may be necessary.

1. The pre-treatment

Pre-treatment can include a belt filter or channel (or inclined belt filter), which is utilized to eliminate floatable and filterable solids from the water through a filter fleece selected to match the solids concentration and viscosity of the wastewater to be dealt with. Pre-treatment by a neutralization plant safeguards the microorganisms that break down organic substances in the wastewater, e.g., in the biological phase of a wastewater treatment plant. Microorganisms respond firmly to fluctuations in the pH esteem. In a neutralized plant, substances, for example, hydrochloric acid or caustic soda are many times used to produce a neutral liquid with a pH of 7 corresponding to that of water.

2. The after-treatment:

In the after-treatment, ultra-filtration can be utilized. In this process, the pores of the semipermeable layer (which can only be penetrated on one side) are more modest than in micro-filtration, however larger than in Nano filtration. In ultra-filtration, the treated dirty or grimy water is forced or constrained through plastic tubes at up to 10 bar bringing about particles, bacteria, and viruses being collected in the pores of the filter tubes. The outcome is totally germ-free water. The membranes are chiefly made of extremely minimal expense materials, for example, cellulose acetic acid derivations or polyamides.

What are the advantages of vacuum distillation Process?

Below we will look at some benefits of Vacuum Distillation:-

A. Lower Operating Temperatures:-

Heat-sensitive compounds are separated or isolated through the technique of vacuum distillation, minimizing or limiting the threat of thermal degradation or disintegrating.

B. Energy Efficiency:-

Operating or Working at lower temperatures can prompt energy savings, as less energy is required to heat the mixture to the lower boiling points accomplished under vacuum.

C. Increased Yield: –

Vacuum distillation expands the yield of desired items by dropping off the boiling points that works with the separation of higher-boiling compounds or mixtures that would some way or another stay in the deposition.

D. Pure and safe products:–

Vacuum distillation can produce unadulterated and safe products. The operation process is simple and requires less gadgets, bringing about high-quality products with high purity.

E. Reduced capital cost:–

Vacuum distillation can lessen the height and width of a distillation column, leading to reduced capital expenses. This makes it a savvy option, notwithstanding slightly higher operating costs.

What are the disadvantages of Vacuum Distillation Process?

Below we will discuss some limitations of Vacuum Distillation

A. Lower Operating Temperatures:-

Heat-sensitive compounds are separated or isolated through the technique of vacuum distillation, minimizing or limiting the threat of thermal degradation or disintegrating.

B. Energy Efficiency:-

Operating or Working at lower temperatures can prompt energy savings, as less energy is required to heat the mixture to the lower boiling points accomplished under vacuum.

C. Increased Yield:-

Vacuum distillation expands the yield of desired items by dropping off the boiling points that works with the separation of higher-boiling compounds or mixtures that would some way or another stay in the deposition.

D. Pure and safe products:–

Vacuum distillation can produce unadulterated and safe products. The operation process is simple and requires less gadgets, bringing about high-quality products with high purity.

E. Reduced capital cost:–

Vacuum distillation can lessen the height and width of a distillation column, leading to reduced capital expenses. This makes it a savvy option, notwithstanding slightly higher operating costs.

What are the disadvantages of Vacuum Distillation Process?

Below we will discuss some limitations of Vacuum Distillation

A. Equipment processing difficulty:–

Vacuum distillation equipment requires a moderate distance between the evaporating surface as well as the condensing surface. This can make the equipment dealing more inconvenient and excessive.

B. Solvent loss:–

During the activity of vacuum distillation, mixtures can be evaporated and solvents can be removed. The brief distance between the evaporation flask and the condenser can bring about solvent loss, which can be challenging to recover.

C. Higher cost:–

Vacuum distillation equipment is for the most part is costly compared to traditional distillation equipment. Accomplishing a high degree of vacuum requires high sealing performance of the materials utilized, which adds to the expense.

What are Vacuum Distillation Process Steps?

The Following steps mentioned below are as per the following:

The diminished crude oil is pumped through a series of heat exchangers and a crude furnace until reaching the ideal temperature (350°C – 390°C).

The decreased crude oil is flashed or blazed to separate the ideal fractions. Light vapors ascend to the top and heavier hydrocarbon liquid fall to the base.

Steam injection at the lower part of the column works on the detachment of lighter boiling components.

The vacuum column utilizes a series of pumps around to keep up with temperature at the right level at specific points along the tower.

Light vapor gases are eliminated at the top of the tower, condensed, and reused back to the column as reflux. Light Naphtha is drawn off and an abundance of gases is sent to flare.

Vacuum gas oil and greasing up(lubricating) oils are drawn off and coordinated for extra treatment in Hydro-treating units.

Vacuum residue from the base is sent to intermediate storage or normally to be additionally processed in an FCC or delayed coking unit.

Where Vacuum distillation Process is mostly used?

A. Vacuum Distillation in Petroleum Refining:-

A complex combination of many different hydrocarbon compounds, petrol crude oil has a carbon atom count going from 3 to 60 carbon atoms for each molecule by and large, in spite of the fact that there might be small amounts of hydrocarbons beyond that reach. The most well-known approach to refining crude oil begins with the distillation of the incoming crude oil in an atmospheric distillation column, which operates at pressures fairly above atmospheric pressure to eliminate impurities.

It is critical not to subject the crude oil to temperatures over 370 to 380 degrees Celsius during the distillation process, since high molecular weight components in the crude oil will initiate thermal cracking and structure petroleum coke at temperatures higher than that. The formation or development of coke would achieve the plugging of the tubes  in the furnace that heats the feed stream to the unrefined petroleum distillation section, which would make the column or section fizzle. Alongside the distillation column itself, plugging would likewise happen in pipping leading from the furnace to the column or section.

To accomplish good vapor-liquid contact, the internals of a vacuum distillation column should keep an extremely low-pressure increase from the highest point of the column to the lower part of the vessel. Along these lines, just products that are withdrawn from the side of the vacuum column are distilled using a distillation plate in a vacuum column. Most of the column packing material is utilized for the fume fluid reaching since pressing material has a lower pressure drop than distillation trays, which brings about a lower pressure drop. This packing material can be either organized sheet metal or randomly dumped packing, for example, Raschig rings, contingent upon the application.

B. Large-Scale Water Purification:-

Vacuum distillation is generally utilized in large industrial plants to eliminate salt from ocean water to produce new water. It is a productive technique for eliminating salt from ocean water. Desalination is the term used to depict this process. Subsequent to being put under a vacuum to bring down its boiling point, and having a heat source applied, the ocean water boils off and condenses, releasing fresh water. At the point when water vapor condenses, it keeps it from filling the vacuum chamber, taking into consideration the effect of running endlessly without a loss of vacuum pressure. The heat generated by the condensation of water vapor is taken out by a heat sink, which utilizes the incoming ocean water as a coolant, in this way preheating the ocean water that is taken care of into the system. A few sorts of distillation don’t utilize condensers, however, compress the vapor mechanically with a pump, which is referred to as vacuum distillation. Basically, this fills in as a heat pump, drawing heat from the vapor and permitting it to be returned to and reused by the incoming untreated water source subsequent to being concentrated. Various sorts of vacuum distillation of water are utilized today, with the most usually utilized being various distillation, Vapor-compression desalination, and multi-stage flash distillation being the most widely recognized.

Conclusion:-

It is the most common way of bringing down the pressure in a column or segment over an organic solvent to a level lower than the vapor pressure of the mixture, creating a vacuum, and causing the components with lower vapor pressure to evaporate from the mixture. The utilization of vacuum distillation can lessen the height as well as the diameter of a distillation column, as well as the general capital expense of the column.

Vacuum distillation is otherwise called “low-temperature distillation” or “low-pressure distillation.” The most common way of refining unrefined petroleum starts with the distillation of the incoming unrefined petroleum in an atmospheric distillation column, which operates at pressures somewhat above atmospheric pressure to eliminate impurities. Vacuum distillation is normally utilized in large industrial plants to eliminate salt from ocean water to produce fresh water. It is a proficient method of eliminating salt from ocean water.

Plastic to Fuel | Pyrolysis Process

Plastic to Fuel | Pyrolysis Process

Plastic to Fuel | Pyrolysis Process

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Plastics are mouldable polymers which can deform to a very high degree. They are a range of organic compounds which are mostly synthetic, derived from petrochemicals. Some plastics are also semi-synthetic in nature and can be made from renewable materials.

Plastics have found wide varieties of use in wide varieties of industries. They are most used in applications of piping, plumbing and vinyl siding. They are also used in automobiles, furniture and toy industries. Medical equipments have found a lot of uses for plastics.

Due to increase in human population, rapid economic growth and continuous urbanization; the use and production of plastics is also increasing very rapidly. Since plastics have a short lifespan of use, this also means that the plastic wastes are also increasing rapidly. Most of the plastics are non-biodegradable hence if they are dumped into the soil then they are going to stay in that area for hundreds of years and will render that piece of land useless for growing crops and even for the sake of urbanization.

If plastics are dumped in the seas then they will float and follow the currents. It has led to accumulation of plastics in various areas of oceans. The accumulation is even as large as size of islands. This poses a threat to the sea life.

Disposal of plastic wastes is a big problem hence it has been recommended time and time again to recycle the plastic materials. Pyrolysis is one way to recycle the plastic material. The basis is that pyrolysis of plastic can be done to produce oil. This oil is then used as a fuel. The method of pyrolysis involves thermal degradation of plastic at different temperatures in the absence of oxygen.

Plastic waste raw material is first obtained and then it is pretreated in order to remain any material which is foreign to the process of conversion of plastic to fuel. In short, impurities are removed from the raw material.

Then the pre-treated raw material is grinded to the required size as desired before inputting the grinded raw material in the reactor, the pyrolysis chamber. The size should be proper so that the reaction is able to occur smoothly and efficiently.

The pyrolysis chamber is loaded with the grinded plastic along with a suitable catalyst in order to promote specific types of chemical reactions. The temperature of the reaction can range from 200-900C based on the quality of the liquid oil desired further down the line as a product. The grinded raw material first gets melted and then it gets vaporized.

The vapors are then passed to condensers in series in order to condense it into a liquid. This liquid is the oil but it is further sent for the process of refining. This refined liquid is the desired oil which is used as a fuel. They are also put into category of biofuels depending on the type of raw material selected. The oil is multipurpose in nature and can also be used in cars.

How to ensure reliable motor operation with variable frequency drives

How to ensure reliable motor operation with variable frequency drives

A variable frequency drive (VFD) is the industry’s standard technique for controlling the speed and torques of induction motors. To ensure reliable operation of motors with VFDs, the user must consider various measures and best practices.

By Cole Casteel, PE, and Taha Mohammed, PE January 17, 2025

Learning Objectives

• Understand the fundamental components and operations of induction motors and VFDs.
• Recognize the key factors for selecting motors and VFDs.
• Grasp important factors for VFD and motor installation.

 

Variable frequency drive insights

• VFDs are gaining widespread popularity for driving motors in industrial and commercial facilities due to their efficiency.
• It’s important that the motor characteristics and application are coordinated with the driven equipment during the motor and VFD selections.
• Monitoring the temperature can help identify VFD problems before they do too much damage.

Induction motors use the principle of electromagnetic induction to convert electrical energy to mechanical energy to rotate or turn the motor shaft. And although a variable frequency drive (VFD) can be integral to efficient motor operation, there are many factors to consider before you install one.

VFDs can be used to adjust the frequency and voltage of the alternating current (ac) power applied to the stator and then control the speed, torque and power of the motor. There are two main control methods that VFDs use to control the operation (speed, torque, power) of an induction motor: vector control and scalar control. While the vector control provides more precise speed control, it is more complex and adds additional feedback devices monitoring the shaft rotation. Thus, the most common and widely control method used is scalar control, also known as volts per hertz or V/f.

The main components of a VFD (see Figure 1) are:

• The ac-dc converter, which converts the incoming 60 Hz ac signal to direct current (dc) using rectifiers or insulated-gate bipolar transistors (IGBT).
• A dc link that smooths the dc signal using capacitors.
• A dc-ac converter that takes the dc and converts it back to ac at the desired voltage and frequency using pulse width modulation (PWM) technique with IGBT transistors.

 

Figure 1: Variable frequency drive block diagram. Courtesy: CDM Smith

As energy saving and more operation controls are desired, VFDs are becoming more widespread for driving motors in industrial and commercial facilities. When using VFDs, there are extra factors and considerations to be taken for a reliable facility and system operation. Understanding and applying these factors will help prolong the lifespan of the motors and VFDs as well as minimizing shutdowns due to unexpected equipment failure.

The following are key factors and best practices to consider when selecting or using motors with VFDs.

How to coordinate VFDs with the driven equipment

For the equipment to operate reliably and properly, it is essential that the motor characteristics and application be coordinated with the driven equipment during the motor and VFD selections. In addition to voltage and phase compatibility of the motor and VFD, the VFD needs to be compatible with the motor and the driven equipment.

One main characteristic is the torque application, for example centrifugal fans and pumps are variable torque application and a normal duty VFD is adequate, while conveyors and positive displacement pumps are constant torque application and require heavy- or severe-duty rated VFDs, which have higher overloading capability.

An additional application to be discussed is the lowest speed the load will be operating at and making sure the motor turndown ratio can accommodate that application and can be safely operated at that low speed without overheating and compromising the operations. For example, a 10:1 turndown ratio for a 3,600 revolutions per minute (rpm) motor is 360 rpm.

Another important item is the motor full load amperage (FLA) and making sure the VFD can provide equal or greater current than the motor FLA. The motor horsepower should not be used to select the VFD and the motor service factor should not exceed 1.0.

Choosing the proper environment for VFDs, motors and drives

Like with anything else in industrial facilities, such as structural supports and pipes or other electrical equipment, motors and drives must be suitably rated for the environments in which they are installed. Process areas in industrial facilities can be subject to physical damage, sprayed or standing water, high humidity, dust, corrosive chemicals and extreme temperatures, all of which can damage or rapidly degrade VFDs containing sensitive electronics.

The VFDs can be protected from their environment with a properly rated National Electrical Manufacturers Association (NEMA) enclosure, such as 4X stainless steel. However, these enclosures come with their own drawbacks. They have larger footprints, add additional cost and make it harder to remove excess heat generated by the VFD. For these reasons, it is recommended to install VFDs in dedicated, climate-controlled electrical rooms (see Figure 2).

Figure 2: Variable frequency drives installed in environmentally controlled room. Courtesy: CDM Smith

Equipment heat degradation

When it comes to electrical and mechanical equipment, one of the biggest reasons for degradation of equipment is heat. The power electronics that make up VFDs generate heat and if this heat builds up within the VFD enclosure, the components can be damaged, operate inefficiently or cause the VFD to shut itself down for protection, forcing equipment downtime. Most VFD enclosures are equipped with fans and air filters to ensure the flow of clean air across the components.

As with home air filters or on-facility heating, ventilation and air conditioning equipment, the air filters will become clogged with particulates and dust, inhibiting airflow. Even when the VFDs are installed in an air conditioned space and the heat cannot escape the VFD enclosure, the damage will be done.

It may seem like a small thing, but changing the air filters on VFD enclosures regularly, as well as verifying the functionality of the fans and ensuring a clear space around the vents can extend the longevity of the VFDs.

When a VFD is installed in a harsh environment, it is important to remember that the NEMA-rated enclosure only provides protection when used and maintained appropriately. For example, a NEMA 3R outdoor enclosure protects the VFD from rain, but if the door is left ajar, it may as well have a NEMA 1 enclosure rating. Enclosures that provide stronger protection (3R, 4X, 7), tend to have more and heavier duty latches and bolts to keep the doors closed.

These are the areas where the environment can do the most damage to the VFD, so it is crucial for the longevity of the drive to make sure the doors stay closed, ensuring the integrity of the enclosure is maintained.

The importance of disconnecting contacts

Safety disconnecting means are required for each motor to be located within sight of the motor location, per NFPA 70: National Electrical Code Article 430.102. However, a code exception is included that allows for the elimination of the motor disconnect if it is impractical or would introduce additional hazards, with an informational note clarifying that motors associated with VFDs meet this condition.

Despite the exception bypassing the need for a separate disconnect, many facilities’ operational staff still prefer to have them, as they can provide a safer working environment allowing technicians to open the disconnect and maintain visuals on the disconnect while they service equipment.

A consideration when including local motor disconnects for motors driven by VFDs is to include auxiliary “break-before-break” or “early break” contacts within the disconnect switch to connect to the VFD and send a signal to the VFD immediately to shut down before the switch is opened. When the motor load is abruptly removed from the load side of the VFD while running, transient voltage and current spikes are created that can damage the transistors in the drive.

Rarely, the damage can be rapid and catastrophic, destroying the drive, but more likely the surges will wear down the VFD electronics, lowering their lifespan. The addition of these auxiliary contacts allows the drive to shut off its output immediately before the load is lost, saving it from unwanted transients. For existing installations without early break contacts, it may be worth stopping the VFD before opening the local disconnect (see Figure 1).

Gauging VFD and power quality

Harmonics in electrical systems are high-frequency sinusoidal currents that get added to the main power wave at multiples of the power frequency (60 Hz). They are created when ac power is converted to dc, which is the first stage of a VFD.

The concern with harmonics is often on their upstream effects, such as increased heating of transformers, nuisance tripping or issues with the electric utility provider. With VFDs, there are also concerns with power quality downstream. As mentioned above, the ac output of a VFD is constructed from the dc bus by PWM, rapidly turning the output transistors on and off. The high-speed switching interacts with the inherent inductance and capacitance of the cable feeding the motor and the motor itself to create what are known as standing waves or reflected waves. The standing waves cause the cables and motor to experience a higher voltage than normal, sometimes higher than the rating of the insulation, causing premature breakdown of the insulation.

There are multiple causes and symptoms involved with power quality issues from the VFD outputs, so there are multiple tools to address them and the best ones will depend on the situation. To minimize reflected waves, it is best practice to keep cable runs between the VFD and the motor as short as possible.

Added length of cable increases the inductance and capacitance, also increasing the magnitude of the reflected waves. The high-frequency noise carried by the cables creates electromagnetic interference (EMI) that can affect nearby analog signals runs with power cable, like pressure or level transmitters signals. Using multiconductor, shielded VFD cable, especially when installed in cable tray or PVC conduit, will make sure those adjacent analog readings are not impacted by the EMI generated in the VFD cable.

With the prevalence of VFDs, industry leaders and motor manufacturers have designed motors with more robust insulation to be used with VFDs, as described in the NEMA MG1 standard and are labeled as inverter-duty.

The VFD output also induces stray currents in the rotor that discharges through the shaft and damaging bearings, causing vibrations bearing failure. To prevent stray currents and the unnecessary vibrations, heating and damage they cause, motors should be equipped with shaft grounding straps, insulated bearings or both.

Whether some of these extra measures are necessary will depend on individual circumstances, such as the VFD manufacturer and technology used, facility layout, motor size and process criticality. Proper protection will curb the negative effects from the PWM output of the VFD and extend the life of the motor.

Other filtering equipment such as sine wave and DV/DT filters may be used to eliminate transients between the VFD and the motor and protect the motor windings from voltage spikes. It is important to consult the VFD and motor manufacturer for recommendations on the proper filtering selection based on individual applications and setup.

Monitoring and protecting VFDs and motors

Similar to VFDs, heat buildup is an issue for the motors. The flow of electrical current is resisted by the motor windings, converting the electrical energy to thermal energy. In a motor, a fan blade is attached to the rear of the shaft to expel hot air while the motor is spinning. This kind of motor construction is called totally enclosed, fan-cooled (TEFC) (see Figure 3) and it works well to remove excess heat from the bearings and stator at rated speed.

Figure 3: Totally enclosed, fan-cooled motor on variable frequency drive with winding thermal protection and safety disconnect. Courtesy: CDM Smith

However, when used with a VFD to reduce the speed of the motor, as the fan is attached to the shaft, it will spin slower, which reduces the effectiveness and allows heat to build up. Generally, it is not recommended to operate TEFC motors below 25% of rated speed without additional cooling or verifying the rating of the motor.

For motors driven by VFDs especially, monitoring the temperature can help identify problems before they do too much damage. The most basic method is to install thermostats constructed from bi-metallic switches around the stator windings. As the two distinct types of metals heat up, they expand at different rates, eventually breaking contact, letting the control circuit know the motor is getting too hot.

However, this discrete signal occurs only after reaching the setpoint and provides no additional diagnostics. Another method is using resistance temperature detectors that continuously vary their resistance as the temperature changes, which can be sensed and monitored remotely, giving more opportunity for proactive intervention to extend the life of the motor (see Figure 4).

 

Figure 4: Cutaway view of an induction motor. Courtesy: ABB

If the facility has a supervisory control and data acquisition system that allows the networking of VFDs via Ethernet or fiber, the additional VFD parameters, signals and statuses can be remotely monitored, such as real-time voltage, current, power, output frequency, motor speed, motor torque and runtimes. This kind of data is valuable for operators and maintenance to ensure the health and longevity of their equipment.

Routine VFD and motor maintenance considerations

All equipment deteriorates over time, so it is crucial to test and maintain it regularly to ensure it remains in good condition. Performing proper maintenance is another key item that enhances the reliability of motors/VFD operations. This includes preventive maintenance and visual inspections, cleaning filters and vents from dust and debris. Motor and VFD inspections include checking for proper ventilations, unusual noises and smells, corrosion and excessive vibrations. Some preventive maintenance measures include applying lubrication, tightening connections and replacing parts.

For detailed maintenance and testing procedures, consider following the manufacturer’s instructions and adhering to the recommended maintenance guidelines from the InterNational Electrical Testing Association and NFPA 70B: Standard for Electrical Equipment Maintenance.

Taha Mohammed, PE, and Cole Casteel, PE, are electrical engineers with CDM Smith.

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Cole Casteel, PE, and Taha Mohammed, PE

Author Bio: Cole Casteel, PE, and Taha Mohammed, PE, are electrical engineers with CDM Smith.

Source:

https://www.plantengineering.com/articles/how-to-ensure-reliable-motor-operation-with-variable-frequency-drives/