The high temperature and low emission electrostatic precipitator ----- is also about EPC general contract of European environmental engineering
High temperature low emission electrostatic precipitator
----- is also about EPC general contracting of European environmental engineering
High Temperature /High Performance Electrostatic Precipitation System
And the turn-key contract of European environment project
Wang Liqian 1 Guo Ling
LAN Guoqiang 2
1. Jiangsu Dongrui Environmental Energy Technology Co., LTD
2. Shenyang Chuangsida
Abstract: In 2008, Jiangsu Dongrui Environmental Energy Technology Co., Ltd. contracted the project of an American multinational company in Oroshaza, Hungary, furnace electric dust collector system. Shenyang Chuangstar Technology (China) Co., Ltd. subcontracted its complete automatic control system. The operating temperature of the electrostatic precipitator is 400~410℃, and the emission concentration is required to be 30mg/Nm3. Since its delivery in September 2009, it has been in continuous operation for two and a half years with good results. According to the Hungarian law enforcement authorities, the actual emission is only 7 mg/Nm3. The system has higher requirements for automatic control and can be fully realized. This project has been well received by users and their parent companies. The results show that the electrostatic precipitator can operate in high temperature environment with high efficiency and low emission for a long time. Through this project, I gained valuable experience in EPC general contracting, and understood the value of strict and serious requirements of foreign countries.
In the context of China's electrostatic dust removal technology level recognized by advanced countries and cheap equipment, in the spring of 2008, a multinational glass container company from the United States visited Dongrui and invited to participate in its Hungarian Oroshaza plant glass furnace electric dust collector project bid. In competition with foreign companies, Dongrui won the general contract and undertook the one-stop service of design, procurement, supply, transportation, installation, commissioning, commissioning, delivery and operation. Tronstar subcontracted the automatic control works for the whole system.
Western companies have stricter requirements for contractors than domestic ones. First, the warranty period is doubled, requiring that the system efficiency does not decline within two years, and the equipment is trouble-free; Second, the safety and health requirements are much stricter, but also much more detailed; Third, there are many detailed requirements for the control of the system that are lacking in domestic projects; Fourth, all equipment and facilities must be certified by the European Union.
Through the cooperation of Dongrui and Tronstar for more than three years, the EPC general contract project was successfully completed, and the project was officially ended in September 2011, and the owner was very satisfied and highly affirmed.
2. Project overview and owner's requirements
2.1 Natural Conditions
Oroshaza city is located 160 kilometers southeast of Budapest, is a scenic tourist small city, there are a number of lakes and hot springs in the city, holidays and weekends there are many local residents or foreign tourists to swim and bathe here, the environment has very strict requirements. In the vicinity of the factory, the main environmental pollutant is the smoke emitted from the glass melting furnace. Therefore, the cleanliness of the atmosphere is very high, and the electric dust collector must ensure that there is no visible smoke at the chimney outlet.
2.2 Properties, characteristics and treatment requirements of smoke and dust
The plant's glass furnaces, which produce 400 tonnes a day, are medium and large in Europe. The flue gas temperature of the glass furnace of the factory is as high as 400~500℃. In view of the vast majority of the operating temperature of the electrostatic precipitator is within 350 ° C, there should be countermeasures for dust above 400 ° C.
The smoke from the plant's glass furnaces is very fine, compared to the hundreds of microns of smoke in power plants, steel plants and cement plants. The particle size is all within 2.5μm, and almost 99% of the smoke is less than 1.0μm. As we all know, the dust with a particle size of 0.1~1.0μm is the most difficult to remove by the electrostatic precipitator.
2.3 Owner's safety protection requirements for electric dust removal system
European factories attach great importance to personal and production safety and health protection. Compared with the domestic, there are many more stringent requirements,
The main points are as follows:
All hardware, including equipment, pipes, components, components, insulation, paint must be certified by the EU safety, marked accordingly.
l All on-site workers and related personnel must apply for life insurance.
l All safety regulations and standards shall adopt EU standards and comply with Hungarian standards.
l There are detailed safety protection requirements for the system design, which are detailed later.
2.4 The Owner's choice of contractor
The owner is a multinational company, the project is selected by its head office contractor, the European headquarters procurement department for specific comparison and selection.
First, the U.S. head office visits the selected companies, and after the contractor is approved, the European head office sends out a tender. After the contractor delivers the tender on time, the European headquarters conducts a comprehensive review and requires the contractor to visit Europe for exchanges, on-site inspections, face-to-face technical disclosure and answer questions. The negotiations on the issues related to technology, construction, commissioning, five-year spare parts guarantee supply, quick handling of emergencies in site operation, payment provisions, project delays or penalties for non-compliance are basically the same as those of general international projects, but the owner is not at ease with China's first general contract, so the procedure is more complicated and the contract requirements are more stringent.
What is more troublesome is that the owner requires: first, if the penalty occurs, the penalty for China should be doubled; Second, the Chinese contractor must have a reliable European partner company in order to represent the Chinese company in the urgent handling of problems arising in the field operation. Third, Chinese workers are not allowed to participate in any construction commissioning work. We carefully studied, promised and did it one by one, and finally, in the competition of European and American companies, we were selected by the European headquarters to sign the system-wide general contract.
3. General project contracting overview
3.1 Design of electrostatic precipitator
According to the above characteristics of dust, the following factors are mainly considered in the design of electrostatic precipitator.
3.1.1 Corona discharge at high temperature
As we all know, when the gas temperature rises, its breakdown voltage decreases, resulting in a reduction in the operating voltage of the electrostatic precipitator, which damages the dust removal efficiency. The design requires a basic judgment of the effect of high temperature.
The corona discharge of a gas is caused by ionization caused by the impact of electrons in the electric field on the gas molecules. The degree to which the electron is accelerated plays a decisive role. The accelerated motion energy obtained by the electron in the electric field is proportional to the electric field intensity and the mean free travel of the electron, while the latter is inversely proportional to the density of the gas. The flue gas temperature rises, the gas density decreases, the average free travel of electrons increases, the energy of electrons increases, the gas breaks down in advance, the operating voltage decreases, and the dust removal efficiency decreases. This is the chain reaction.
Quantitatively speaking, the energy that causes the gas breakdown is inversely proportional to the square of the temperature, and the gas breakdown voltage is inversely proportional to the gas temperature. Therefore, as the temperature rises, the energy input to the electric field will drop more. According to this law, in order to generate plasma by corona discharge, increasing the temperature is extremely effective; But from the point of view of dust removal, the temperature rise, it is very unfavorable.
For the coal-fired power plant of the largest user of the electrostatic precipitator, the flue gas temperature is mostly 130 ° C (403°K) above and below, and the same pole distance is 400mm, if the installation is good, the breakdown voltage of the electrostatic precipitator can reach more than 65kV. According to the above inverse law, the breakdown voltage will be reduced to about 40kV when the temperature is 400 ° C (673°K). In other words, for every 10℃ increase in temperature, the breakdown voltage is roughly reduced by 1kV. The influence of this on electrostatic dust removal is obvious. In addition to structural problems, the quantitative effects of voltage reduction at high temperature were estimated when designing the high temperature electrostatic precipitator.
3.1.2 High temperature material selection
The electrostatic precipitator is used for high temperature flue gas of 400℃ and above, which is rarely seen at home and abroad, and what material is used to make it becomes an important issue whether it can run safely for a long time.
As we all know, the commonly used carbon structural steel grade is named according to the yield point. The so-called yield point is that when the steel is stretched, when the stress exceeds the elastic limit, even if the stress is no longer increased, the steel still continues to undergo plastic deformation (yield), and the minimum stress value when the plastic deformation is obviously produced is the yield point. For example, Q235, its yield point is 235MPa. In addition, we also know that the elastic modulus of ordinary structural carbon steel will be significantly reduced at 350~400 ° C, that is, the same stress will cause a larger strain of steel at this time. In order to avoid obvious deformation when used, the allowable stress of the steel should be reduced in the design, which will increase the amount of steel and the engineering cost, which is not economical.
Therefore, when designing this electrostatic precipitator that works at 400~410 ° C, it is necessary to find a steel whose yield point and allowable stress are higher than Q235 and whose price is still lower, which can work safely and normally at 400~410 ° C, while basically not increasing the engineering cost, and avoid the use of stainless steel that is expensive although it is resistant to high temperature. For this reason, we turned our eyes to "Corten steel". It is a relatively new type of steel, cost-effective. Compared with the Q235-A used in conventional electrostatic precipitator, the advantages are obvious:
Yield point: Q235-A----235MPa, Corten-A----343MPa
Tensile strength: Q235A----370MPa Corten-A----480MPa
Therefore, it is decided to use it on the shell force components of the electrostatic precipitator, such as columns, girders, ring beams and important suspension components of the electrode. The materials of other components are listed in Table 2. Among them, 95% high-aluminum porcelain is very necessary for high-voltage insulation parts, and ordinary electric porcelain is insufficient in temperature resistance and will fracture due to thermal stress.
3.1.3 The smoke is very fine
Whether it is a coal-fired power plant, cement plant, or iron ore sintering plant, a large part of its dust belongs to mechanical dust production, and the particle size is coarse, tens to hundreds of microns, accounting for a large proportion. The dust of this project is all combustion dust, and the particle size is much finer than that of mechanical dust, 98.8% are sub-micron, 36.2% is less than 0.25μm. According to the charging mechanism, in this particle size interval, both the collision charge and the diffusion charge are quite weak, and the efficiency of the electrostatic precipitator will be naturally limited. In addition, the vibration of fine dust flying loss is serious, but also very unfavorable. The difficulty of charging is difficult to change, and can only be compensated by increasing the dust collection area. In order to reduce vibration flying, choose a lower flue gas flow rate.
3.1.4 Dust has good electrical conductivity
In the dust composition, Na2SO4, which conducts electricity well, accounts for 85%, and K2O is 1%. Medium Ca2SO4 and MgSO4 accounted for 10%. Only 3% of SiO2 and NaCl are unfavorable to the operation of electrostatic precipitators. The electrostatic precipitator does not have the problem of high specific resistance back corona, nor does it have the problem of sodium salt adhesion and stress corrosion, which is very advantageous.
3.1.5 Design parameters of electrostatic precipitator
3.2 System Design
The owner attaches great importance to the safety and reliability of the system and the convenience of maintenance. In addition, European labor is expensive, and the wages of on-site workers are more than 20 times that of China, so some targeted measures are taken in the design:
l In order to prevent overtemperature damage to the equipment, set the cold air inlet, the baffle control and temperature measurement chain, automatic/manual control. The cold air inlet is also used for rapid cooling of the system during emergency maintenance.
The electrostatic precipitator and the induced draft fan are equipped with a flue gas bypass, and the switched flue gas baffle is pneumatic to prevent the failure to operate in case of power failure. Emergency switching must be automatic and send an alarm signal.
l All the operating equipment and baffles can be integrated into the automatic control system and can be controlled and displayed on the spot.
In order to prevent blockage, an inspection door must be set up every 10m in the pipeline. Inspection doors should also be set up in front of each bend and in front and behind each flue gas valve.
l The manhole doors, hand doors, inspection doors and on-site monitoring instruments of all equipment and pipelines must have facilities that can be safely reached by people, including walkways, platforms, stairs, handrails, etc.
Each operating equipment, including flue gas valves, must be equipped with local buttons or switches in addition to being able to be started, stopped and switched in the control room. For longer transport machinery, there should also be local switches every 10m. The flue gas valve should have a visible switching signal.
l When the furnace changes fire or the combustion condition fluctuates, the speed of the variable frequency speed regulating induced draft fan must be kept constant to prevent accidents.
l System noise is not greater than 50db(A). In order to reduce noise, the induced-draft fan uses an efficient backward-curved blade impeller and is equipped with a muffler. Fan bearing cooling water cooling, water temperature monitoring.
l All steel structures, including ESP base, flue support, platform, stairs, handrails, etc. are hot-dip galvanized. All bolted connections, screw holes precisely drilled in the factory, no need for on-site welding.
l Thoughtful thermal expansion compensation measures.
3.3 Automatic Control System
The whole electric dust removal system is controlled by PLC, and the control room is located in the room surrounded by the steel support space below the electric dust collector. Set Touch
Two screens, respectively installed on the heating and unloading control cabinet and vibration cabinet, can display, control, record the main functions and parameters of the whole system and alarm.
The control signal is sent to the furnace process control room by means of Ethernet glass fibers. Upper DELL computer and LCD display bit
Next to the process control computer, it can also display, control, record the main functional parameters of the whole system and alarm. The main interface is shown in Figure 3. The main data of electrostatic precipitator are displayed on the process control host at the same time.
l Power cabinet, 1 set. Power module PS307.
l Electrostatic precipitator high pressure control cabinet, 3 sets.
l Electric dust collector heating, dust discharge control cabinet, 1 set. LV circuit. The control system DELTA touch screen is installed on this cabinet.
l Electrostatic precipitator vibration control cabinet, 1 set, located on the top of the electrostatic precipitator, LV loop.
l Induced draft fan frequency conversion control cabinet, 1 set. Control 132kW motor revolution.
l 1 interlocking control box, hung on the wall of the control room.
lUPS Standby power supply.
The upper DELL computer and LCD display are placed in the main control room of the melting furnace.
l 1 air conditioner.
3.3.2 Control Software
l Operating software MICROSOFT WINDOWS XP SP2,
l Program software SIEMENS STEP7 V5.3,
l Configuration software SIEMENS WINCC6.2,
3.3.3 Control Objects
l air mixing valve. Can be remote control, remote automatic control and local hand control.
l Smoke damper. There are 5 baffles to control the inlet and outlet of the induced draft fan and the electrostatic precipitator and the bypass of the electrostatic precipitator. Can be remote control, remote automatic control and local hand control.
l Induced draft fan. Control start, stop, speed change; Keep the fan constant speed when the furnace is changing fire; Monitor bearing temperature.
l Electrostatic precipitator. The high voltage cabinet controls the high voltage power supply and grounding of the 3 electric fields of the electrostatic precipitator, and the LCD touch screen displays the control parameters. Low pressure cabinet controlled heating unloading ash.
l Electromagnetic vibrator. Control the vibration cycle and intensity of 62 electromagnetic vibrators, remote control, remote automatic control or local manual control.
l Star ash discharge valve. Control the start and stop of 3 star ash discharge valves, remote control or local manual control.
l Screw conveyor. Low pressure cabinet control start stop and heating, remote control or local manual control.
3.4 Construction, installation and commissioning
The installation of the complete system was subcontracted to KIS, Hungary. The company has installed chemical, coal-to-gas and cloth bag dust collector devices, and has no experience in installing electric dust collectors. But the work is serious, under the guidance of the Chinese side, the installation is completed in about 5 months, and the quality is high. Hungary's short history of opening up to Europe and the United States, its more than 10 people in the installation team can speak English only 2 people, communication difficulties, but also affected some progress.
In fact, it is more accurate, strict and scientific to test the installation quality by whether the V-A curve is coincident:
A slightly experienced installation and debugging personnel know that when adjusting the anode and cathode distance, it is not difficult to make the breakdown reach 70,000 volts. In good weather, even if the polar distance error is as large as 40~50mm, it is completely unqualified, and it is not difficult to boost the no-load voltage to 70kV. The simple examination of electric field breakdown voltage will often cover up the defects of installation quality.
l Parallel T/R boost although generally not high voltage device damage, but there is a potential danger. Spare parts for this purpose seem superfluous.
Using the principle of "several of the same electric field boost V-A curves should be exactly the same and consistent with each other" to test the installation quality, the installation requirements are more stringent, and it is more difficult to achieve conformity than a single test breakdown voltage. And this qualification should have been achieved, and no one artificially raised the standard.
The lV-A curve method eliminates the workload of parallel T/R in the field.
When lT/R specifications are selected, they often exceed the normal operation needs of the electric field and artificially increase the rated voltage and current, one of the considerations is to facilitate the parallel no-load boost test. The over-specification T/R will lead to the increase of flashover frequency, the decrease of automatic voltage regulation quality, and the waste of funds. The V-A curve method can be used to select the T/R specifications on demand, eliminating the mismatch of the horse car.
We use this method to test the quality of electric field installation is also an "innovation"! Although it has also happened during installation and commissioning
When there is debris left in the electric field, the voltage cannot rise. However, due to the overall good installation quality, after the removal of debris, the V-A curves of the three electric fields coincide very well during the acceptance of the voltage boost test. It is because there is no one-sided pursuit of the boost breakdown value, without temporary prying, breaking, and other brutal measures to make up for the installation of the excessive, this electrostatic precipiter in two consecutive years of high temperature operation, the anode and cathode without large stress deformation, to achieve stability and efficiency, which is a valuable experience.
3.4.2 Spring base of induced draft fan
In order to reduce vibration and noise, the induced draft fan is equipped with a spring base. The design is that the fan shell, bearing box and motor base are fixed on an integral steel frame, and the spring base is placed under the steel frame, and the spring base is fixed on the concrete foundation. However, the technical person in charge of the owner mistakenly recognized that the spring is more capable of absorbing shock directly under the fan and the motor, and asked for changes according to his requirements. Results During the trial operation, the fan shell and the motor shaft-impeller system shook greatly respectively, which cracked the insulation shell of the shell. Change the spring position and fix the shell to solve the problem. Two years of continuous uninterrupted operation, indicating that the quality of the induced draft fan is good.
3.4.3 Cold Air Valve
During debugging, it is found that the design of the cold air inlet is too large, the baffle has just opened, and the cooling has reached the predetermined value, resulting in poor linearity of regulation. Because it can still be used, it is no longer changed, and the owner has also approved.
3.5 Test, acceptance and operation
In September 2009, the electrostatic precipitator system was commissioned and put into trial operation (equivalent to 168 hours of trial operation), and the naked eye observed the chimney outlet, completely unable to see the smoke, and the sky is as blue. The full-time agency under the municipal government of Szeged, Hungary's second largest city, went to the factory for testing on September 28 (Figure 4). The measured results show that the emission from the chimney mouth is less than 10mg/Nm3, and the long-term emission is about 6~7mg.Nm3, which is less than the guaranteed value of 30 mg.Nm3. At this point, the EPC general contract project of the electric dust collector system passed acceptance and was officially put into operation.
3.6 Project Return visit
After the electric dust collector was put into operation, there were no problems in continuous operation for two years, and good dust removal efficiency was maintained, and dust emission was not increased, and long-term, continuous and efficient operation was achieved, and the owner was very satisfied. In June 2011, almost two years before the official operation, the factory sent a project quality certification letter, affirming the success of the general contract project (Figure 5).
On November 22, 2001, we went to Hungary for a return visit, and the director of the plant once again told us that the electrostatic precipitator had been running for two years without interruption, no overhaul, and no reduction in efficiency. And they also summed up a lot of operational management experience.
We also visited the European headquarters of our head office, and they were very satisfied with this project, the first EPC contracted by a Chinese company, and believe that it opens the door for future cooperation.
Step 4 Summarize
Although this is a small project, but the five organs are complete, the implementation also encountered many unexpected difficulties in domestic projects,
Through the cooperation of our two companies, one by one. Through this complete general contracting practice, it is shown that:
The electrostatic precipitator can run efficiently for a long time at a high temperature of 400 ° C, without the application of expensive heat-resistant steel.
The electrostatic precipitator achieved an emission of less than 10mg/Nm3 for 85% of the dust that is submicron.
l was the first general contractor for the air pollution control project of a multinational company in an advanced country, overcoming technical problems under harsh conditions, using a European company as a subcontractor, accumulating knowledge and operational experience, and achieving success.
Practice shows that Chinese environmental protection companies basically have the ability to go out independently and can contract foreign projects by EPC.
Step 5 Give thanks
I would like to thank Mr. Kjell Porle, former Chairman of the International Commission on Electric Dust Removal, for his enthusiastic help in the general contracting process.