How to calculate compressed air dryer energy consumption ~ refrigerated & desiccant?

Writer： admin Time：2022-10-26 00:00:00 Browse：371℃

At the outlet of air compressor, the compressed air is saturated or supersaturated moist air. But many industries have requirements for compressed air pressure dew point. Therefore, it is necessary to install compressed air dryers. At present, the main types of air compressor dryer are refrigerated and desiccant air dryer. When choosing a compressed air dryer, need to consider its operation energy consumption. This article will analyze the energy consumption parameters of various types of air compressor dryers. And put forward the relevant calculation formula.

1. Compressed air dryer working principle:

The content of water vapor in compressed air is related to pressure and temperature. And understanding how it works helps in analyzing dryer energy consumption.

(1) Refrigerant air dryer working principle:

It uses a refrigeration unit to cool the compressed air. Then it reaches a certain dew point temperature. Finally, the dryer will discharge the moisture in it. Thereby drying the compressed air. The refrigeration equipment is a compressor. For a detailed introduction, see this article:how refrigerated air dryer works.

(2) Desiccant air dryer working principle:

The desiccant beads have a unique affinity for water vapor. So it can absorb the moisture in the compressed air. Firstly let the air come into full contact with the adsorbent. Water molecules in the air will diffuse to the adsorbent. Therefore, moisture will be adsorbed. At the same time, there are molecular motions and collisions. So some of the water molecules will leave the adsorbent. They are back in the air again. The amount of adsorption and desorption of water molecules in a certain period of time is equal. At this time, it reaches dynamic equilibrium.

This balance bases on a certain temperature and pressure. When they change, the original equilibrium relationship will be destroyed. It gradually establishes a new balance.

Assume that the temperature does not change. The amount of water absorbed by desiccant beads varies. It will increase with the increase of the pressure of water vapor. Also assume that the pressure is constant. Its water absorption decreases with increasing temperature. For the desorption process, the effect of temperature change is much larger than that of pressure change. In short, moisture is adsorbed at low temperature or high pressure. Moisture is desorbed at high temperature or low pressure. The adsorption dryer generally adopts the twin tower type. One tower performs adsorption and the other tower performs desorption. Desorption is also namely regeneration.

In addition, desiccant dryers have different regeneration methods. So it contains multiple types. That is, heatless, micro heated, blower purge, compression heat. Of course, there is also another combination air dryer. Thus, different desiccant compressed air dryer, different energy consumption.

2. Air compressor dryer applications:

The application range of each dryer is shown in Table 1. In addition, its technical parameters are listed in Table 2.

(1)Table 1 “Dryer Application Range Table”

CompressedAirDryerType	PressureDewPoint(℃)	EquippedAirCompressorType
Refrigerantairdryer	3~10	non-centrifugalaircompressor
Desiccantairdryer(heatless,heated)	(-20/-40/-70)	non-centrifugalaircompressor
Combinationaircompressordryer	(-20/-40/-70)	non-centrifugalaircompressor
HOCtypeairdryer	(-20/-40)	Centrifugaloroil-freeaircompressor(exhausttemperature notlowerthan110℃)

(2) Table 2 ” Dryer technical parameter table”

AirCompressorDryerType	RegenerationType	Cycle Time (h)	Regeneration AirLoss (%)	Pressure Loss(%)	EnergyConsumption Factor
Refrigeratedairdryer	&mdash;&mdash;	&mdash;&mdash;	&mdash;&mdash;	<5	refrigerationcompressor, coolingfanorwater,pressureloss
Heatlessadsorption dryer	smallregenerationairis usedforpressurerelief desorptionandadsorption wasteheattoheatup	0.167	&le;21~27.6	<3	airconsumption,pressureloss
Miroheateddesiccant airdryer	smallregenerationairis slightly heated, and then performpressure reliefdesorption	2~6	&le;12~15.8	<3	airconsumption,pressurelossand electricheater
Microairconsumption blowerpurge regenerativeairdryer	Heatatmosphericair fordesorption.Then usesmallregeneration air blow cooling.	6~8	&le;3~4	<3	airconsumption,pressurelossand electricheater
Zeroairconsumption blowerpurge regenerativeairdryer	Heatatmosphericairfor desorption.Thenuse small regeneration air blow cooling and recovery.	6~8	0	<3	coolingwater,pressurelossand electricheater
Microairconsumption HOCtyperegenerative airdryer	Recycle high temperature airattheoutletofthe aircompressor.Anduseit fordesorption.Thenuse small regeneration air blow cooling.	6~8	&le;3.5~5	<7	coolingwater,pressurelossand airconsumption
Zeroairconsumption HOCtyperegenerative airdryer	Recycle high temperature air at the outlet of theaircompressor.Anduse it for desorption. Then use small regeneration air blow coolingandrecovery.	6~8	0	<7	coolingwater,pressureloss

Some companies need low compressed air dryer energy consumption. So you can choose the zero air loss dryers.

3. How to calculate compressed air dryer energy consumption ?

To sum up, the main energy consumption of refrigerated air dryer is three parts. Namely refrigerant compressor, cooling fan or cooling water, pressure loss. And energy consumption of desiccant air dryer includes the following five parts. That is, regeneration air, pressure loss, electric heater, external heating device and energy consumption of cooling water.

Assume that the air compressor air flow is Q, m 3 /min; the discharge pressure is P, bar; the input power is N, kW; the annual operating hours of the air dryer areh, h.

(1) Calculation of energy consumption for regeneration air of compressed air dryer

Nqh = N*h*Ka*t1/T —— Formula (1)

In formula (1): Nqh is the energy consumption caused by the regeneration air, kWh; and Ka is the percentage of the regeneration air consumption; t1 is the regeneration air consumption time in a cycle, h; In addition, T is the regeneration cycle period, h; If the air consumption is the average air consumption, then t1=T.

(2) Pressure loss energy consumption calculation

The operating rule of the air compressor is as follows. For every 1 bar increase in exhaust pressure, energy consumption will increase by about 7%. Therefore, the energy consumption caused by the pressure loss of compressed air dryer is: Nyh = 0.07P*N*h*Kp —— Formula (2).

In formula (2): Nyh is the pressure loss energy consumption, kWh; in addition, Kp is the dryer pressure loss percentage.

(3) Electric heater energy consumption calculation

For micro-heat and blower purge adsorption dryers, it also needs to add the energy consumption of electric heaters. That is, Nrh = Nr*h*t2/T —— formula (3).

In formula (3): Nrh is the energy consumption of the electric heater, kWh; Nr is the power of the electric heater, kW; t2 is the regeneration air heating time in one cycle, h; in addition, T is the regeneration cycle, h.

(4) Energy consumption calculation of external heating device

For the blower purge desiccant dryer, it also needs to calculate the energy consumption of the air blower. That is, Nfh = Nf*h*t3 /T —— formula (4).

In formula (4): Nfh is the energy consumption of the blower, kWh; Nf is the power of the blower, kW; t3 is the working time of the blower in one cycle, h; T is the regeneration cycle period, h.

(5) Cooling water energy consumption calculation

For dryers that need to be cooled by cooling water, it also needs to caculate the energy consumption of cooling water. That is, Nsh = K*Qs * (Hk + Hb )*h/(367η1*η2 ) —— formula (5).

In formula (5): Nsh is the cooling water energy consumption, kWh; K is the margin coefficient. Its general value is 1.05 ~ 1.2; Qs is the cooling water volume, t/h; Hk and Hb are the lifts of the open-type water pump and the closed-type water pump, t/h; η1 is the pump efficiency; in addition, η2 is the motor efficiency.

Nsh can also be calculated using a simple formula. That is, Nsh = 0.2Qs*h —— formula (6).

In formula (6): Qs is the cooling water volume, t/h.

The above are the formulas for calculating the energy consumption of compressed air dryer.

4. Dryer energy consumption calculation example:

There is a 600 kW air compressor. Its air capacity is 100m³/min. At the same time, the working pressure is 7 bar. And assume that its annual operating hours are 6000 h. The known parameters of each type of dryer are shown in Table 3.

Parameter	Refrigerant Dryer	Heatless Dryer	Heated Dryer	Combination Dryer (Heatless)	Blower Purge (MicroAir Loss)	Blower Purge (ZeroAir Loss)	HOC Dryer (MicroAir Loss)	HOC Dryer (ZeroAir Loss)
Cycletime(h)	——	0.167	6	0.33	8	8	8	8
Heaterpower(kW)	——	——	36	——	54	54	——	——
Heatingtimeof onecycle(h)	——	——	4	——	5	5	5	——
Coolingfan /compressor/ blowerpower (kW)	23	——	——	13.8	13	13	——	——
Workingtime offan /compressor/ blowerduring onecycle(h)	——	——	——	0.33	5	8	——	——
Regenerationair (%)	——	21	13	9	4	0	5	0
Coolingwater (t/h)	14.6	——	——	14.6	——	12	37.5	75
Pressureloss (%)	5	3	3	8	3	3	5	5.5

According to the above parameters, use the previous corresponding formula to calculate. The results are shown in Table 4.

Parameter	Refrigerant Dryer	Heatless Dryer	Heated Dryer	Combination Dryer (Heatless)	Blower Purge (MicroAir Loss)	Blower Purge (ZeroAir Loss)	HOC Dryer (MicroAir Loss)	HOC Dryer (ZeroAir Loss)
Regenerationair	——	75.6	43.2	32.4	5.4	0	6.75	0
Pressureloss	8.82	5.292	5.292	14.112	5.292	5.292	8.82	9.702
Heater	——	——	14.4	——	20.25	20.25	——	——
Coolingfan /compressor/ blowerpower	13.8	——	——	8.28	4.875	7.8	——	——
Coolingwater	1.752	——	——	1.752	——	1.44	4.5	9
Totalannual energy consumption of compressed air dryer	24.372	80.892	62.892	56.544	35.817	34.782	20.07	18.702

To sum up, the energy consumption of different compressed air dryer varies greatly. Therefore, the operating energy cost of the dryer cannot be ignored.