There is an established industry standard specifying that compressed air systems operating with on-site pressure dew points below 0°C require the use of desiccant air dryers. However, technical proposals from multinational corporations in this field often advocate for the direct adoption of desiccant air dryer solutions, arguing that this approach can result in a more streamlined system architecture and lower capital expenditure.
However, the combination of a refrigerated air dryer and a desiccant air dryer is also highly popular in the market. How can one differentiate between these two solutions? Let’s dive into a detailed explanation from both technical and commercial perspectives.
Technically, the primary factor to consider is the water vapor load in the dryer. We then recommend suitable product models by taking into account the on-site conditions of the users. Subsequently, we assess and compare the differences between these two solutions in terms of the overall cost over the product's entire life cycle.
1. Technical Analysis
· Design Input Conditions
When determining the input performance parameters of a refrigerated air dryer, one can refer to the National Standard JB/T 10526-2017, Refrigeration Compressed Air Dryers for General Use. Specifically, consider the specified operating condition A2 at full load, as stated in Table 1.
The customer's requirement for the downstream pressure dew point is -20℃.
· Water Vapor Load Analysis
2. Preliminary Conclusions
The water vapor load of the pre-refrigerated air dryer accounts for 82.89% of the total load, while the condensate load of the post-desiccant air dryer accounts for 17.11%. As the inlet temperature increases, the proportion of the load handled by the refrigerated air dryer tends to rise. When expanding the inlet temperature range to ensure broader applicability of this load distribution, it is generally accepted that the pre-refrigerated air dryer handles 85–90% of the water vapor load, while the post-desiccant air dryer accounts for 10–15%.
A single desiccant air dryer accounts for 100% of the total load.
3. Comparison of Dryer Selection Options
When choosing a combined dryer, special attention should be paid to the selection of the refrigerated air dryer. In addition to the inlet flow rate, key parameters such as ambient temperature, inlet air temperature, and inlet pressure must be considered. These parameters are used to determine the appropriate correction factor, ensuring the correct selection of the refrigerated air dryer. This approach guarantees that the selected unit operates within its normal performance specifications (pressure dew point of 2–10°C). In contrast, selecting a desiccant air dryer is more straightforward. The primary parameter to consider is the inlet pressure. If the pressure falls within the standard 7 bar range, an appropriate model can be easily selected by referencing the product catalog based on the flow rate. If the pressure deviates from this standard, the necessary pressure correction should be applied to finalize the selection.
When choosing a combined dryer, there are two additional advantages:
First, when the air capacity remains constant but the water vapor load of the desiccant air dryer varies, the water vapor load in a system with a pre-refrigerated air dryer is only 10–15% of that in a system without one.
Second, with a pre-refrigerated air dryer, the desiccant air dryer benefits from the reasonable layout of the combined system, resulting in a relatively low inlet temperature for the desiccant air dryer, which enhances its drying effect.
A single desiccant air dryer option lacks the advantages mentioned above. During the selection process, in addition to considering the inlet pressure correction, the inlet temperature correction must also be taken into account. Once the inlet temperature exceeds 50°C, the desiccant air dryer will no longer function properly.
In addition, choosing the combined dryer offers another advantage. During the cold and dry autumn and winter seasons, the refrigerated air dryer can be turned off, allowing the desiccant air dryer to operate independently.
Referring to Table 3, taking an air capacity of 55 Nm³/min as an example.
We list the operating parameters and converted power consumption of different models. It is evident that the total power consumption of the air compressor system equipped with the combined dryer is significantly lower.
Note:
1.Taking the performance parameters of our refrigerated air dryer and desiccant air dryer as an example, it may vary slightly among products from different companies.
2.The specific power of the air compressor is set at 6.5 kw/(m³/min), corresponding to a pressure of 7 barG. These values may vary slightly according to the performance characteristics of different air compressors.
3.Average Air Consumption Power= Flow Rate*Average Regenerated Air Consumption*Specific Power
4.Heater Power Consumption=Cycle Heating Time*Heater Power
5.Calculation is based on 8,000 hours per year and an industrial electricity cost of 1 yuan per kWh
4. Comparison of Investments over the Full Life Cycle
When comparing the advantages and disadvantages of different solutions based on the comprehensive costs over the full life cycle of the products, and referencing the listed selling prices of our products as shown in Table 4, we can draw the following conclusion:
The combination dryer is more advantageous than the single desiccant air dryer.
In specific terms, the table clearly indicates that, compared to a single desiccant air dryer, the combined dryer can achieve cost parity in less than a year. Once cost parity is reached, the combined dryer will yield greater savings in subsequent operations. The electricity cost savings mentioned above are calculated based on continuous operation for 8,000 hours throughout the year. Interested readers can perform their own calculations for verification.
Users are advised to conduct technical and economic comparisons and then make a choice according to specific conditions to achieve an optimal solution.
Proper operation of the dryer is a crucial prerequisite for obtaining the desired compressed air, reducing regeneration energy consumption, and extending the equipment's service life. Users are advised to conduct technical and economic comparisons and make their choice based on specific conditions to achieve the optimal solution.
Source: The R&D Center of EPSEA Industry
