Electrostatic precipitator (ESP) is a filtration device that removes fine particles, like dust and smoke, from a flowing gas by the force of an induced electrostatic charge minimally impeding the flow of gases through the unit. In contrast to wet scrubbers, which apply energy directly to the flowing fluid medium, an ESP applies energy only to the particulate matter being collected and therefore is very efficient in its consumption of energy.
Types of ESP:
1. Dry type Electrostatic Precipitator
Dry Electrostatic Precipitators (ESPs) can be used in many industries for various applications for cleaning of dust laden industrial gases. ESPs can handle any volume of gases and many types of dusts with high removal efficiencies. The continuous improvement in design & engineering of the ESPs reduce the operating costs by reducing the energy consumption, maintenance cost and lower downtime. The ESP components are well designed by using most advance technologies..
The dust laden gases are passed through the electrical field consisting of profiled collecting electrodes and discharge electrodes. The discharge electrodes are charged with negative high voltage and the collecting electrodes are earthed. The gas is equally distributed and made to pass through these gaps of electrodes across width and length.
The discharged electrodes emit electrons when charged with high negative voltage. These negative electrons accumulate on dust particles and thus dust particles are charged negatively. The charged dust particles are attracted towards the profiled collecting electrodes. When the dust particles touch the collecting electrodes, it loses its charge, but due to agglomeration, they still stick to the plate. These electrodes are cleaned with the use of robust tumbling hammer type rapping system. Independent rapping systems are used to clean the collecting as well as discharge electrodes.
Our ESPs are optimally designed, tailor-made to suit the customer operating conditions. The migration velocity is an extremely important parameter to decide the size of the ESP and helps to determine the efficiency. Apart from this, there are many parameters which affect the sizing of the ESP such as:
- Electrical resistivity of the dust
- Dust content at inlet & outlet of ESP/strong>
- Chemical composition of dust & gas
- Particle size of dust
- Temperature of gas
- Humidity in gas
ESP consist of following components:
- Inlet Cone with gas distribution screen
- Outlet cone
- Collecting Electrodes, Discharge electrodes
- Suspension system for Collecting Electrodes & Discharge electrodes
- Pent house which houses support insulators
- Independent Tumbling Hammer type rapping system for Collecting Electrodes & Discharge electrodes
- HV system including TR sets
The dust laden gas enters the ESP through the inlet cone. Here the gas velocity is reduced substantially and is distributed evenly across the cross-section of electrical field with the help of gas distribution screen which are mounted in inlet cone.
Further, the gas enters the first electrical field of ESP. The electrical field consists of collecting electrodes and discharge electrodes, which are suspended from top and are electrically separated with the help of support insulators. The collecting electrodes are placed at 400 mm. The dust particles get charged and gets attracted towards collecting electrodes. The collected dust is dislodged through the impact given at the bottom of the collecting electrodes. Each row of the collecting electrodes is cleaned separately with help of tumbling hammer type raping system. To avoid back corona of discharge electrodes, a separate tumbling hammer type rapping system is provided above the discharge electrodes suspension system.
When the hammer impacts the collecting electrode row, it creates jerk and the dust layer is dislodged from the surface. With the help of profile, it gets guided to slide down to the collecting hoppers. Thereafter, depending on the dust conveying system, it gets transported to the storage system of the plant.
Depending on the application and other various design parameters, the ESP has number of fields to achieve the desired cleaning efficiency. Each field has different current ratings to catch the finer particles. The coarser dust particles are easy to ionize and hence gets separated easily. But the finer particles require more current to charge and hence more numbers of fields are required so that the partially charged particles can get charged in next field and can be separated from the gas stream. Hence, it draws more current.
The dislodged dust gets collected in the hopper. It is further discharged through Rotary air lock valve either to mechanical conveying system or pneumatic conveying system.
While leaving the gas from the last field, more than 99% of the dust is separated and clean gas is sent out of ESP in guided way to avoid turbulence. A gas screen is provided at outlet to trap the last fine particles which were not able to get attracted to collecting plates.
The other main important component of the ESP is High Voltage Equipment, commonly known as Transformer Rectifier (TR Set), which determines & controls the strength of the electrical field generated between the discharge & collecting electrodes.
- Microprocessor controlled
- ESPs come with Inspection doors at the bottom of each field.
- Walkways between each field for inspection purpose.
- Access from the ESP roof to insulators, rapping mechanism and suspension system.
- Current limiting factor
- Accurate recording of signal
- Diagnosis of sparks & arcs
- Optimal power supply for changing demand of power
- Modulation of half waves for highly resistive dust
- Simple failure diagnosis reports
- Easy to understand and operate
Safety Interlock system:
ESPs are designed considering all human safety features. All the access & inspection doors, electrical equipment TR sets & TR control systems are interlocked using castle key lock system. This ensures & avoids any uncontrolled entry inside the electrical field as well as handling of any electrical equipment.
- Rigid Pipe & Spike type discharge electrodes.
- Sturdy & durable collecting electrodes for longer life.
- Separation of ultra-fine dust particles to meet the required lower emission norms.
- Continuous dust collection process.
- Low pressure drop (approx. 2.5 mbar) at high degree of separation.
- Low maintenance due to few and slowly rotating components.
- Low energy costs compared to Fabric Filter separators.
- Can handle large volume of gas flow, virtually there is no upper limit.
- Handling high gas temperatures.
- Individual solutions possible by adaptation of the standard construction to the local conditions.
- Maintenance and services ensuring continuous operation of the plant.
2. Wet Electrostatic Precipitator
Tar Precipitator also termed as Wet Electrostatic Precipitator. The Wet Electrostatic Precipitator compliments our product range with an extremely versatile de- dusting system that is perfect for any process in which special dust or gas characteristics make dry separation difficult or impossible.
The Wet ESPs are unbeatable since many years in view of operational safety, long life cycle and high collection efficiency. They are well suited for precipitation of finest dust with dust afflicted water drops of aerosols and emissions containing tar or oil. Another, positive effect is the additional bound of toxic elements (for example HCL, SO2, NaCL & HF)
The Wet ESP also works on the principle as of dry ESP. Here too, a high voltage is applied between discharge electrode and collecting plates. The dust gets ionized and gets separated from the gas flow.
The processed gas enters the wet ESP horizontally at the bottom and is spread uniformly across the entire cross section by means of gas distribution system. In this case, like in case of dry type ESP, the collecting electrodes are replaced with honeycomb type tubes, which acts as collecting plates. The SS discharge electrodes are placed at the Centre of these honeycomb type collecting tubes
High voltage is applied between the discharge electrodes and collecting plates/tubes. Due to ionization, the dust particles in the gas flow gets separated and agglomerate to the existing dust on the collecting surface. This dust is periodically cleaned with the help of washing system. The cleaning liquid is flushed at the bottom of the ESP along with the dust particles. A system consisting of valves, piping and nozzles are provided for that purpose. The purified gas is released from the hood of the wet ESP. In case, non- stop working of wet ESP is required, a parallel wet ESP is to be installed with same capacity.