01

What are the characteristics of domestic cold dryer compared with imported cold dryer?

At present, the hardware configuration of domestic cold dryer parts is not much different from that of foreign imported machines. Refrigeration compressors, refrigeration accessories and refrigerants are widely used by international famous brands. The user applicability of the cold dryer is generally more than the imported machine, this is because the domestic manufacturers in the design, production of cold dryer has fully taken into account the characteristics of domestic users, especially the climatic conditions and daily maintenance characteristics. For example, the refrigeration compressor power of domestic cold dryer is generally larger than that of imported machines of the same specification, which fully adapts to the characteristics of China's vast territory and large temperature differences in different regions/seasons. In addition, the domestic machine is also quite competitive in price, and has an incomparable advantage in after-sales service. Therefore, the domestic cold dryer is quite popular in the domestic market.

At present, the gap between domestic cold dryer and imported cold dryer is mainly manifested in the production process level, especially in the refrigerant system pipeline cleaning, assembly and welding, etc. In addition, the imported green environment-friendly refrigerant R134a, which has no destructive effect on the atmospheric ozone layer, is now commonly used, which is still difficult to achieve on domestic cold dryers.

　　02

What are the characteristics of the cold dryer compared with the adsorption dryer?

Compared with adsorption drying, freeze dryer has the following characteristics:

There is no gas source consumption, for most of the gas source users, the use of cold dryer than the use of adsorption dryer to save energy;

② No valve wear;

③ There is no need to add or replace the adsorbent regularly;

④ Low running noise;

Daily maintenance is relatively simple, as long as the time to clean the automatic drain filter can be;

⑥ There are no special requirements for the pre-pretreatment of the air source and the supporting air compressor, and the general oil-water separator can meet the requirements of the air intake quality of the cold dryer;

The cold dryer has a "self-cleaning" effect on the exhaust, that is, the content of solid impurities in the exhaust gas is less;

⑧ While discharging the condensed water, part of the oil vapor can also be condensed into liquid oil mist and discharged with the condensed water.

Compared with the adsorption dryer, the "pressure dew point" of the cold dryer for compressed air treatment can only reach about 10 ℃, so the drying depth of the gas is far less than that of the adsorption dryer. In the technical community has formed a selection practice: when the "pressure dew point" requirements at zero, the first cold dryer, when the "pressure dew point" requirements at zero, adsorption dryer is the only choice.

　　03

How to get compressed air with very low dew point?

The dew point of compressed air after treatment by cold dryer can be about -20 ℃ (normal pressure), and the dew point after treatment by adsorption dryer can reach above -60 ℃. However, some industries that require extremely high air dryness (such as the microelectronics industry requires a dew point of -80°C) are obviously not enough. At present, the method promoted by the technical field is to connect the cold dryer and the adsorption dryer in series, and use the cold dryer as the pre-pretreatment equipment of the adsorption dryer, so that the moisture content of the compressed air is greatly reduced and then enters the adsorption dryer, so that the compressed air with extremely low dew point can be obtained. Moreover, the lower the temperature of the compressed air entering the adsorption dryer, the lower the dew point of the finally obtained compressed air. According to foreign information, when the inlet temperature of the adsorption dryer is 2 ℃, the dew point of the compressed air can reach below -100 ℃ using molecular sieve as adsorbent. This method has also been widely used in the country.

　　04

Cold dryer and piston air compressor matching should pay attention to what?

The piston air compressor is non-continuous air supply, and the air flow pulse is generated at work. The air flow pulse has a strong and lasting impact on the components of the cold dryer, which will lead to a series of mechanical damage to the cold dryer. Therefore, when the cold dryer is connected with the piston air compressor, a buffer air storage tank shall be set at the downstream side of the air compressor.

　　05

What should be paid attention to when using the cold dryer?

Pay attention to the following matters when using the cold dryer:

① The flow pressure and temperature of the compressed air shall be within the allowable range of the nameplate;

The installation site should be ventilated, less dust, there is enough heat dissipation and maintenance space around the machine and can not be installed outdoors to avoid rain and direct sunlight;

The cold dryer is generally allowed to be installed without foundation, but the ground must be leveled;

④ should be as close as possible to the user point, to avoid the pipeline is too long;

⑤ There should be no detectable corrosive gas in the surrounding environment, especially pay attention to not being in the same room with ammonia refrigeration equipment;

The cold dryer pre-filter filtration accuracy should be appropriate, too high precision is not necessary for the cold dryer;

⑦ The inlet and outlet pipes of cooling water shall be set independently, especially the outlet pipe shall not be shared with other water cooling equipment to avoid drainage obstruction caused by pressure difference;

⑧ Keep the automatic drainage device unblocked at any time;

Do not start the cold dryer continuously;

⑩ The parameter index of the compressed air actually processed by the cold dryer, especially when the intake air temperature and working pressure are inconsistent with the rated value, should be corrected according to the "correction coefficient" provided by the sample to avoid overload operation.

　　06

What is the effect of high oil mist content in compressed air on the operation of the cold dryer?

The exhaust oil content of air compressors is different. For example, the exhaust oil content of domestic piston type oil lubricated air compressors is 65-220mg/m, the exhaust oil content of less oil lubricated air compressors is 30-40mg/m, and the exhaust oil content of domestic so-called oil-free lubricated air compressors (actually semi-oil-free lubrication) is 6-15mg/m. Sometimes, due to the damage and failure of the oil separator in the air compressor, the oil content in the air compressor will greatly increase, after the compressed air with large oil content enters the cold dryer, a thick oil film will be covered on the surface of the copper tube of the heat exchanger. Because the heat transfer resistance of the oil film is 40 to 70 times larger than that of the copper tube, this greatly reduces the heat transfer performance of the precooler and evaporator, and in severe cases, the cold dryer will not work properly.

The specific performance of the evaporation pressure decreased and the dew point instead of rising, the oil content in the exhaust of the cold dryer increased abnormally, and the automatic drain was often blocked by oil. In this case, even if the oil removal filter is continuously replaced in the pipeline system of the cold dryer, it will not help, and the filter element of the precision oil removal filter will soon be blocked by oil. The best way is to repair the air compressor and replace the filter element of the oil and gas separator to make the exhaust oil content reach the normal factory index.

　　07

How to correctly configure the filter for the cold dryer?

Compressed air from the gas source contains a large amount of liquid water, solid dust with different particle sizes, oil pollution, oil vapor, etc. If these impurities are allowed to enter the cold dryer directly, the working condition of the cold dryer will deteriorate. For example, oil pollution will pollute the heat exchange copper pipes in the precooler and evaporator, affecting heat exchange. Liquid water increases the working load of the cold dryer, and solid impurities are easy to block the drain holes. Therefore, it is generally required to install a pre-filter upstream of the air inlet of the cold dryer for impurity filtration and oil-water separation to avoid the above situation. The filtration accuracy of the pre-filter for solid impurities is not very high, generally 10 ~ 25μ, but the separation efficiency of liquid water and oil is better.

Whether the post filter of the cold dryer is installed shall be determined by the user's quality requirements for compressed air. For general power gas, a main line filter with high precision can be used. When the gas requirements are higher, the corresponding oil mist filter or activated carbon filter should be configured.

　　08

What should I do if I want to make the exhaust temperature of the cold dryer very low?

In some special industries, it is not only necessary to use compressed air with low pressure dew point (I. e. water content), but also to require the temperature of compressed air to be very low, that is, to use the cold dryer as a "dehydration air cooler. The measures taken at this time are:

① Cancel the pre-cooler (air-air heat exchanger), so that the compressed air forced to be cooled by the evaporator cannot be heated back,

②At the same time, calculate the refrigeration system, and increase the power of the compressor, the heat exchange area of the evaporator and condenser when necessary. (The simple method commonly used in practice is to use a larger size cold dryer without a pre-cooler to process a smaller flow of gas.

　　09

What measures should be taken for the cold dryer when the intake air temperature is too high?

The intake air temperature is an important technical parameter of the cold dryer. All manufacturers have obvious restrictions on the upper limit of the intake air temperature of the cold dryer, because the high intake air temperature not only means an increase in sensible heat, but also the water vapor contained in the compressed air The content has also increased.

JB/JQ209010-88 stipulates that the air inlet temperature of the cold dryer does not exceed 38 ℃, and many famous foreign cold dryer manufacturers also have similar regulations. Arguably, when the air compressor exhaust temperature exceeds 38 ℃, a rear cooler must be added downstream of the air compressor to reduce the compressed air temperature to the specified value before entering the aftertreatment equipment.

The current situation of domestic cold dryers is that the allowable value of the air intake temperature of the cold dryers is continuously improving. For example, ordinary cold dryers without pre-coolers began to increase from 40 ℃ in the early 1990 s. At present, ordinary cold dryers with an air intake temperature of 50 ℃ have appeared. Regardless of whether there is commercial speculation, from a technical point of view, the increase in intake air temperature not only reflects the increase in gas "sensible temperature", but also reflects the increase in water content, which is not a simple linear relationship between the increase in load of the cold dryer. If by increasing the power of the refrigeration compressor to compensate for the increase in load, the cost is far from cost-effective, because in the normal temperature range, the use of rear cooler to reduce the compressed air temperature is the most economical and effective approach. The high temperature air intake type cold dryer is to install the rear cooling container on the cold dryer without changing the refrigeration system, and the effect is very obvious.

　　10

In addition to temperature, what are the requirements for the environmental conditions of the cold dryer?

The influence of ambient temperature on the work of the cold dryer is very large. In addition, the cold dryer has the following requirements for its surrounding environment:

Ventilation: especially for air-cooled cold dryer is especially necessary;

Not too much dust;

③ There can be no direct radiant heat source on the use site of the cold dryer;

④ The air should not contain corrosive gases, especially ammonia can not be detected.

Because ammonia is in a water environment. It has a strong corrosive effect on metal copper. Therefore, the cold dryer should not be installed with ammonia refrigeration equipment.