Efficiency analysis of centrifugal air compressor

1、 Isothermal efficiency section

The basic pneumatic design of centrifugal air compressors has been analyzed through various theoretical techniques and verified through actual production. It is a process of striving to approach the theoretical ideal value. Theoretical data and actual data (mainly indicators: flow rate, pressure, energy consumption) are mutually confirmed and developed. Therefore, after years of summarizing, exploring, and improving, it is very important for the design and production of centrifugal air compressors; This is also the significance of Changweifu Road having relatively mature prototype models. Of course, this is also the reason why many inexperienced brands cannot completely solve technical problems from the principle.

Efficiency is the core fundamental parameter of centrifugal air compressors; No matter how exquisite the equipment is, how strong the brand effect is, or how cheap the price is, if the overall efficiency of the machine is not high, it is a serious loss for customers.

Air compression, three states1. Isothermal compression; 2. adiabatic compression; 3. Variable compression; According to the principle, isothermal compression is the most energy-efficient compression method for gas compression, and centrifugal air compressor is a device that is close to isothermal compression state.

Isothermal compression efficiency, commonly known as isothermal efficiency, is an important indicator for measuring the overall efficiency of a centrifugal air compressor.

Isothermal compression energy Lis

Isothermal efficiency η=-----------------------

          Shaft power Lp

 Note:1. Isothermal compression work, after knowing the design conditions (design atmospheric pressure, design temperature, humidity), flow rate (m³/min）、 The situation of exhaust pressure can be theoretically calculated;

     2. Shaft power Lp=gas compression work+mechanical loss+thermal radiation;

Under the design conditions of Changweifu Road centrifugal air compressor in Vietnam project: atmospheric pressure101KPaA, Inlet temperature 35Degree, humidity85%Volume flow rate 5000Nm³/h, exhaust pressureUnder the premise of 0.8MPaG, the isothermal compression work is obtained361.1KW;

Based on their own design, manufacturing level, and a large amount of actual equipment testing data, organize and calculate the shaft power522KW±4%；

           361.1KW

Isothermal efficiency η 1=-----------------------=69%

           522KW

          361.1KW

Isothermal efficiencyh1=-----------------------=66.5%

        （522*1.04）KW

Note:

1. In theory, each bidder, under the premise of unified bidding parameters, should perform isothermal compression workLis is the same, this is a theoretical calculation data. If individual brands take5000m³/hequal5000Nm³/hTo calculate the isothermal compression work, the isothermal compression work is directly smallerAt 20%, the isothermal efficiency would be outrageously high.

2. My technical personnel believe that the equipment we provide, due to the use of mature pneumatic models and larger heat exchanger chambers (reducing inter stage resistance) compared to foreign products, is able to achieve66.5-69%At this flow rate and pressure, the isothermal efficiency is already the highest efficiency product in the industry.

3. Theoretical ideal isothermal efficiency:70-71%, this is the lifelong pursuit of a centrifugal air compressor designer.

4. What we submittedThe shaft power of 522KW has reached the isothermal efficiency69% is almost close to the theoretical maximum efficiency value. If some brands submit shaft power lower than 522KW, it is necessary to carefully review their relevant parameters.

give an example1: Assuming the submitted shaft power is576KW， Isothermal efficiency:

           361.1KW

Isothermal efficiencyor=-----------------------=62.8%

         576KW

This isothermal efficiency is better thanWe calculateof66.A value of 5% is more than 4% lower; 

give an example2Assuming the submitted shaft power is500KW， Isothermal efficiency:

           361.1KW

Isothermal efficiencyor=-----------------------=72.2%

         500KW

This isothermal efficiency can be considered false, and it can be concluded that the shaft power is inappropriate. We need to be vigilant and carefully review their parameters; 

According to the principle of centrifugal air compressor, the ideal theoretical maximum value of isothermal efficiency is approximately75%about，The smaller the gas volume, the lower the isothermal efficiencyThe 5000Nm3/h model has a rated temperature efficiency of 665-69% is almost the highest value in the industry.

2、 Selection of installed power

Rated design point of centrifugal air compressor5000Nm³/Axis power of h:522KW±4%,

Maximum shaft power:543KW；

Maximum shaft power at 105% flow rate:570KW；

             Selection of installed power:580KW

               Future theoretical hanging meter power:570KW/0.952=598KW；

vigilantSF1.15 is a number game;

If someoneRated design point of centrifugal air compressor5000Nm³/Axis power of h:522KW±4%,SF1.15

Maximum shaft power:543KW；SF1.15

Maximum shaft power at 105% flow rate:570KW；SF1.15

                     Selection of installed power:580KW；SF1.15

                 Future theoretical hanging meter power:（570KW/0.952）*1.15=687.2KW；

This is it.The logic of SF1.15;

Motor nameplate power580KW， However, once there is SF115 means this is a machine580*1.15=667KW main motor;

Why are you doing thisEveryone knows that 522KW is an excellent shaft power value. If we don't write it this way, there will be almost no chance to participate in bidding. What's intolerable is that our own energy consumption is indeed 1% higher5%So, write 522KW without error, and then use SF1.15 is used to switch concepts and achieve the goal of passing the assessment.

That's also why some projects have motorsSF1.1 is such a strange service coefficient; Energy consumption is 10% higher than normal equipment, and the energy consumption index is written according to normal equipment,SF1.1. It is used to switch concepts.

Summary:

1. Isothermal efficiency70-71% is the ideal theoretical maximum value for centrifugal air compressors, and it is also the lifelong pursuit of centrifugal air compressor designers. The hospital will use this value as benchmark data to analyze the isothermal efficiency and energy consumption of each household, which will be clear at a glance.

2. vigilantSF1.The destructive effect of the coefficient of 15 in the technical agreement is due to the signing of the technical agreement and energy consumption assessmentThe key.

3、 Efficiency comparison among different companies

           361.1KW

Isothermal efficiencyor=----------------------- =           %

         shaft power

According to the shaft power reported by each brand, the isothermal efficiency can be calculated. Due to the deviation of shaft power, it can be calculated separately for comparison.