Five problems in design and selection of air compressor units for fermentation
1 Introduction With the development of the market economy, foreign advanced sets of electric power centrifugal centrifugal air compressor units for fermentation have been selected by more and more enterprises. According to the engineering practice in recent years and the preparation of competitive international bidding procurement technical documents, some experiences and lessons have been accumulated, which are now compiled for reference and reference.
2 power consumption
2. 1 Definition of power consumption: The ratio of the shaft power input to the compressor to the volumetric flow rate per minute. It can be known from the definition that the specific power consumption represents the energy consumption level of the unit, and it can be difficult to grasp in practical applications because of the complicated situation.
2. 2 shaft power of the compressor
2. 2. 1 The shaft power of the compressor is different due to the different structure of the compressor. There are several situations:
2. 2. 2 Domestic E1 series models, the main unit consists of main motor + coupling + gear speed increaser + coupling + compressor.
2. 2. 3 Imported unit, the main unit consists of main motor + coupling + gear speed increaser + compressor.
2. 2. 4 The shaft power input to the compressor is not included in the efficiency of the main motor, and the coupling loss of the main motor output shaft end is not counted. Whether to account for the coupling loss of the gear speed increaser and the gear shaft output shaft end is determined by structural factors.
2. 2. 5 Obviously, the shaft power of the compressor cannot fully characterize the energy consumption level of the whole machine.
2. 3 volume flow
2. 3. 1 The technical specification provides three definitions of volumetric flow.
2. 3. 1. 1 inlet volume flow (m3 / min): The flow rate determined under suction conditions such as pressure, temperature, compressibility, humidity and gas composition at the inlet flange of the compressor.
2. 3. 1. 2 Actual volumetric flow rate (m3 / min): The flow rate at a state determined by conditions such as temperature and pressure on any given section. Since the term is used to describe the flow at many locations, the actual volumetric flow cannot be used interchangeably with the inlet volumetric flow.
2. 3. 1. 3 Standard volume flow [m3 / min (N) ] : The pressure measured in any section is converted to 0. 1014MPa (A), the temperature is converted to 15.56 °C and the compressibility coefficient is 1.0. The volumetric flow rate corresponding to the dry gas state. In the unit of measurement: A - represents absolute pressure; N - represents standard state.
2. 3. 2 Actual volume flow rate
2. 3. 2. 1 Pressure, temperature, humidity and test position have an impact on the volume flow. Without the given conditions, the data in the quotation obtained is difficult to compare and evaluate.
2. 3. 2. 2 Temperature (1) Folding temperature. When a given condition is required to be quoted according to the standard volumetric flow rate, the problem encountered is that the standards implemented at home and abroad are different, and the standard temperature values ​​defined by the project are also different. The values ​​used are: 0 °C; 15.56 °C; 20 °C; up to 4 values ​​at 25 °C. It should be calibrated according to the standard temperature defined by physics, ie 0 °C. This value needs to be clearly written in the bidding documents.
(2) The temperature of the inlet should be given according to the average value of the high temperature of the day.
2. 3. 2. 3 Pressure (1) The pressure of the label, after the request is given, there is no objection.
(2) The inlet pressure should be given by the sum of the local summer atmospheric pressure minus 2 times the final resistance of the conventional imported purifier group. The measured negative pressure value before the inlet guide vane of the compressor is about 10 KPa.
2. 3. 2. 4 Relative humidity can be taken from the buyer's local zui hot or ziu wet weather data, the absolute absolute moisture content of the data.
2. 3. 2. 5 Measurement position (1) The flow measurement at the air inlet, due to the limitation of the pipe diameter and the field conditions, the straight pipe section required by the meter cannot meet the requirements, and the corresponding measurement accuracy cannot be guaranteed.
(2) Measure the flow rate at the exhaust port. When the unit is equipped with an aftercooler, it can be used at the outlet of the aftercooler to meet the position measurement required for the straight pipe section.
(3) It is recommended to measure the pressure, temperature and flow rate of the exhaust gas at the straight pipe section of the aftercooler outlet, which needs to be clearly written in the bidding documents. The flow measured at this location is accounted for by the flow loss of the condensate. The measured pressure has been factored into the head loss of the aftercooler.
2. 4 Project examples
2. 4. 1 Problems in the preliminary quotation In the initial quotation, the compressor power shaft dispersion interval is also very different between 1600 - 2100 kW. The aggregated data cannot be compared and evaluated. The problems found have been reviewed in the previous section.
2. 4. 2 Data and requirements given in the actual international procurement bidding documents.
2. 4. 2. 1 given data (1) air;
(2) Atmospheric pressure: 0. 09592MPa (A);
(3) Inlet pressure: ≤0. 09530 MPa (A) (after filter);
(4) Inlet air temperature: 36 °C;
(5) Relative humidity: 80%;
(6) Standard volume flow: 550 N m3 / min (1 standard atmosphere, 0 °C, dry air, measured at the outlet of the aftercooler);
(7) Exhaust pressure: 0. 35 MPa (A) (aftercooler outlet);
(8) Exhaust gas temperature: ≤36 °C (cooling inlet water temperature 28 °C, fouling coefficient water side ≥0. 35m2 · K / kW, aftercooler outlet);
(9) Inlet flow: ?m3 / min (data provided by the bidder);
(10) Compressor shaft power: ?kW (data provided by the bidder);
(11) Specific power consumption < 3. 6 : ?kW/ Nm3 / min (data provided by the bidder).
2. 4. 2. 2 Basic requirements Consider the efficiency of isothermal compression and the wide range of stable operating conditions, requiring secondary compression, with intercooler units.
2. 4. 3 The price data of the quotation book is shown in Table 1:
2. 4. 4 Summary
2. 4. 4. 1 From the bidder's data summary table, it can be seen that domestic equipment and foreign equipment have a large gap in energy consumption level, which is the main reason why foreign companies can occupy the market.
2. 4. 4. 2 Compared with the power consumption, when the parameters are given properly, the combined data can be obtained.
2. 4. 4. 3 It should be noted that in the technical annex of the contract, it is necessary to specify the details of the manufacturer's test bench and the user's on-site verification and confirmation, which will be part of the payment terms for the commercial contract.
3 Selection of self-controlled actuators
3. 1 Research on domestic users
3. 1. 1 Around 2002, five users were interviewed and the domestic and foreign manufacturers of self-control actuators were selected pneumatic actuators.
3. 1. 2 Pneumatic actuators In general, the user is satisfied with the use. When the instrument air purification and pressure dew point values ​​meet the specifications, the pneumatic actuator itself is generally less problematic.
3. 1. 3 instrument air source
3. 1. 3. 1 The user who has the instrument air source air compressor station can guarantee the quality and reliability of the instrument air source.
3. 1. 3. 2 The instrument air source for the complete set of construction of the main engine is not reliable enough. This is mainly the standard adopted by the host. The domestic "JB/T6443" centrifugal compressor is equivalent to the American Petroleum Institute standard "API617": "The compressor and auxiliary equipment described in this standard shall be designed and constructed to ensure their service life. At least 20 years; uninterrupted operation time of at least 3 years. This is a recognized design principle. "The air compressor and dry cleaning device of the instrument air source do not have such demanding requirements, and the reliability cannot meet the requirements. It makes sense.
3. 1 electric actuator
3. 2. 1 In the engineering example described in this paper, the user does not have the instrument air source air compressor station. If the host computer is equipped with a pneumatic actuator, it must be specially equipped to construct the instrument air source system.
3. 2. 2 Discard the optional pneumatic actuator based on the following considerations.
3. 2. 2. 1 The instrument air supply system specially designed for the host is not reliable.
3. 2. 2. 2 The construction space of the instrument air source system is limited by the site conditions and is not reasonable to solve.
3. 2. 2. 3 Increase construction investment and difficulties in building units.
3. 2. 2. 4 Considering the operation, management and maintenance of the instrument air source, the construction unit also requires that the electric actuator be considered under the premise of ensuring reliability.
3. 2. 3 Use of electric actuators
3. 2. 3. 1 The electric actuator has three sets of mainframes for the following purposes:
DN800, 1 electric inlet guide vane, constant pressure to adjust volume flow.
DN300, 1 electric butterfly valve for surge protection.
DN125, 1 electric control valve for surge adjustment.
3. 2. 3. 2 After more than a year of operational practice, the electric actuator has not had any problems so far.
3. 2. 3. 3 The main set of electric actuators, which meet the required reliability and can simplify the complexity of the system, should be able to give preliminary confirmation.
4 Control the non-stop switching of dual power supply
4. 1 Actual operating fault conditions
4. 1. 1 High-voltage-controlled high-voltage electronic control has very few problems. The reason for the shutdown is mostly the external grid voltage fluctuation, which causes the main motor to lose pressure and protect the machine from stopping.
4. 1. 2 Control the power supply Low-voltage control power supply, the fault caused by various reasons is far greater than the high-voltage electronic control. In order to reduce the frequency of downtime, the old unit has been modified to control the automatic switching of dual power.
4. 2 Terms of the Contract Technical Attachment “The control system has a dual power automatic switching device. The buyer guarantees that there is at least one power supply at any time.â€
The buyer proposed to add the words “with non-stop switching†to this clause. The seller believes that this device is not needed for shutdown switching, and the meaning is very clear. Zui did not modify the terms.
4. 3 Problems in commissioning When controlling the running unit, the automatic switching of the dual power supply is confirmed, the automatic switching can occur, but in the process of automatic switching, the running unit will lose power due to the instantaneous power supply of the control power supply. The protection is down.
4. 4 Dispute and resolution of the problem
4. 4. 1 Beginning of the foreign commissioning engineer, there is no requirement for non-stop switching in the terms of the contract technical annex. The final problem of zui was solved as requested by the buyer.
4. 4. 2 In the process of implementing the terms of the contract, the two parties will inevitably have problems. In the event of a problem, the words of the contract terms will be used. The meaning of this lesson is in the contract terms: the words “no downtime†cannot be omitted.
4. 4. 3 The old unit does not have microcomputer control, and the dual power supply switching device is controlled without stopping. It allows instantaneous power loss. The new unit is equipped with a fully automatic microcomputer automatic control system. It is not allowed to control the instantaneous power loss of the power supply. Switching the power loss during the control of the power supply, and adding an online UPS, the problem has been solved simply and effectively.
5 Surge protection and surge regulation
5. 1 Basic requirements for the characteristic curve The energy head* quantity characteristic curve should rise continuously from the rated point to the expected surge point. When the flow rate is greater than 10% of the scheduled surge flow rate, the compressor should be able to work continuously without opening the bypass line.
5. 2 manual unit protection
5. 2. 1 The old unit has a low degree of self-control, and the regulation relies on manual and experience. It can be considered that there is only surge protection and no surge adjustment function.
5. 2. 2 Without surge regulation function, during the process of opening or stopping the antibiotic production system, a large amount of compressed air is vented by bypass, causing waste and environmental noise pollution. However, years of operational practice have shown that manual regulation is not economical, but it is safe.
5. 3 Self-control of surge protection
5. 3. 1 There are a variety of surge protection systems that can be selected as required. Usually the following functions should be implemented:
5. 3. 1. 1 Use the PLC to control the surge line to avoid surge.
5. 3. 1. 2 If surge occurs, turn off the compressor.
5. 3. 1. 3 The basic parameters of surge control are:
The discharge pressure ladder is too high; the discharge pressure line is too high; the main motor load current is too small.
5. 3. 2 Engineering exceptions
5. 3. 2. 1 One expansion project selected one single-stage compressor unit with a high degree of automation. After commissioning and delivery, it often stopped.
The shutdown record of the single board machine is called up. The reason for the * shutdown is that the exhaust temperature exceeds the limit of 220 °C, and the unit protection action stops.
5. The current of the motor is 5. 8kV, and the 6kV voltage of this factory is 6. 6kV. There are two reasons for the voltage instability: First, the impact of the voltage fluctuation of the public network, the impact does not exceed 5% of the rated value; Second, the impact of changes in the size of the main transformer load.
When the unit is running stably, the operating condition of the unit has not changed, but the load current of the main motor is reduced and the set value of the small load current is approached. After setting the small load current value of the main motor, as a surge signal, the unit immediately enters the unloading condition, that is, the intake valve is throttled, the bypass valve is opened and vented, and the exhaust temperature is 165 in 20 minutes. °C rises to the 200 °C alarm limit until the 220 °C parking limit, and the protection stops.
5. 3. 2. 3 There is another factor. The high exhaust pressure of the Zui before the exit of the machine is 0. 20MPa (G). When running in parallel with other units, the inlet pneumatic butterfly valve has a opening of only 50. % is 45° and fully open is 90°. The unit can not be fully loaded, and the load current of the main motor does not go up, which further aggravates the frequency of occurrence of surge protection malfunction.
5. 4 Engineering Special Case Discussion
5. 4. 1 Negotiation has no result, the reason is very simple, voltage instability is the user's own business, of course, the user must solve the problem of voltage instability. If the voltage is to meet the requirements of the unit, the user can't do it, and the seller thinks that he has no responsibility, which has created a situation that both sides are embarrassed.
5. 4. 2 The quality and assurance level of power supply in different regions of the country are different. One thing is common, that is, factory companies can only be subject to the monopoly power supply system. Based on this, it can be considered that the single-factor surge protection mechanism is not suitable for national conditions, at least not perfect.
5. 4. 3 The principle for solving this problem is precaution. That is, in the bidding documents, the power supply conditions and the magnitude and range of the voltage change are explicitly written, and the unit is required to have a stable operation within a given voltage range. When there is no practical data, it can be given as 6kW + 10% or 10kV + 10%.
5. 4. 4 It is a special case to say that this situation is not seen and there are related reports.
This high voltage situation is obvious when the antibiotic production system just started driving. This is because the utility power system has been put into operation, but it is in a slight load state, and only one unit of the air compressor system is operating under the micro load state. This is for the factory's own high-voltage power distribution system. If the high voltage is taken directly from the public network, the voltage level is naturally determined by the power quality of the public network.
5. 5 Surge protection and surge regulation
5. 5. 1 The origin of the problem was in the bidding and contract negotiation, and at the previous technical exchange meeting, the buyer believed that the surge protection included the function of surge regulation.
In the deep communication in the execution of the contract, when the buyer explicitly requires the unit to have a flow rate from 0 → 110% of the rated value (undervoltage operation), both have optimized energy-saving adjustment performance, both sides understand the terminology and concept. A deviation has occurred.
5. 5. 2 The seller’s opinion
5. 5. 2. 1 The seller believes that surge protection and surge regulation are two concepts. Although surge protection also has a certain surge regulation function, the main function is to protect the safety of the unit.
5. 5. 2. 2 The technology is mature to meet the buyer's requirements, but at an additional cost. The seller’s contract price meets the requirements of the bidding documents and technical annexes to the contract.
5. 5. 3 Configuration block diagram for surge protection and surge regulation
5. 5. 3. 1 Surge protection
5. 5. 3. 2 Surge protection plus surge regulation
5. 5. 4 The effect of the actual zui small steady flow is 48% of the rated volume flow. The regulation is stable.
5. 5. 5 It is recommended that the requirements for surge protection and surge regulation be included in the bidding documents and contract technical annexes.
6 Automatically controlled DCS system
6. 1 Survey situation
6. 1. 1 Visited the new unit users in recent years. The unit's opening and stopping needs to be manually operated in the control cabinet next to the machine. The computer in the duty room usually has an automatic inspection display data, but there is no graphic display interface. .
6. 1. 2 The control cabinets next to the machine are usually small screen LCD screens. The required data still needs to be adjusted. It is not intuitive and not convenient.
6. 2 The buyer's request The control cabinet next to the machine, that is, the function of the main control microcomputer, can be realized on the microcomputer of the operation duty room, and the graphic display interface of the man-machine dialogue function should be provided on the microcomputer of the operation duty room.
6. 3 DCS system to meet the buyer's requirements, you need to use DCS system that is centralized management of distributed control system, the conventionally used PLC system is called centralized management centralized control system.
6. 4 Usage
6. 4. 1 When starting the unit, the operator with the operation authority, after typing the password, click the start button with the mouse, the DCS system will enter the startup self-test procedure, if the monitoring meets the start condition, the main motor is 60 seconds. Electric, the main motor star point is closed at 80 seconds, the liquid soft start device is cut off, and the host smoothly enters the normal running state. After the operator exits the startup program, the person who does not have the operation authority cannot input commands to the microcomputer, and can only access different graphical interfaces.
6. 4. 2 In the shutdown or running state, the post-cooler outlet pressure can be arbitrarily modified between 0.13 - 0. 25MPa (G), of course, the pressure rise can only be achieved if the system capacity is sufficient. Constant pressure self-controlled gas supply.
7 Conclusion
7. 1 There are still several problems such as: constant temperature automatic control of lubricating oil, application of environmental protection oil mist remover, two-way automatic switching of main oil pump, control practice of environmental noise, and the reappearance of the measured performance curve of the manufacturer's test bench at the user site. Confirmation and other issues will be discussed in subsequent articles.
7. 2 I hope this article can provide some reference and help to the peers; I hope that the domestic manufacturers can catch up and emotionally choose to use domestically produced units, but the market economy is only about the survival of the fittest and not about feelings.
Christmas decoration and gifts
Cute Christmas Decorations,Animal Christmas Ornaments,Christmas Decorations,Christmas Decorations Ornaments
COFCO HEBEI INTERNATIONAL TRADING CO., LTD. , https://www.cofcohb.com