Reliability

AAC facilities are costly and time consuming to install. The most dangerous machine in these systems is the autoclave. Consider a metal piece that lengthens and shortens by at least 30 mm (related to the full length of an autoclave) in each process. Therefore, the reliability of autoclaves must be carefully monitored from the design stage until installation, and care must be taken against any possible automation errors or cover safety negligence. Kotsa shares expert design experience for such autoclaves, and based on this experience installs a reliable automation software. The autoclave experts provide the necessary activities for future failure prevention and maintenance during the installation phase. All these activities will be customized based on facility and production workflow requirements.

Condensate in autoclaves

When steam encounters a cooler surface, it loses some of its heat. This heat loss creates small water droplets called condensate. Even in cases where the steam system is very well insulated, heat loss always occurs along the line and as a result, condensate is formed. Water (condensate) accumulates in the lowest locations in the system and this accumulated water is then discharged by the steam trap to maintain heat or to keep the steam in the process as dry as possible. There are five main reasons that can result in high quantities of condensate:

·     The autoclave is (too) large and therefore has a lot of cold surfaces that the steam comes into contact with.

·     The autoclave is outside of the closed area of the factory, so that the maximum body temperature will be the ambient temperature. The resulting temperature varies slightly depending on the condition and thickness of the insulation, but this factor is ignored in the calculations.

·     Due to the length of the autoclave, the steam travels approximately 50 meters inside the autoclave.

·     The load is (too) high.

·     Applying a vacuum to the inside of the autoclave from the beginning of the process.

Different systems have different characteristics, but another factor influencing the potential increase in condensate is the distance between the autoclave and the steam system. Increasing this distance will cause the amount of condensate to increase.

After the steam transfers the high temperature to the product in the autoclave, it quickly turns into condensate. Failing to remove the condensate quickly can have the following consequences:

·     The remaining condensate (water) inside the autoclave will support the development of more condensate. 

·     The product surface will be covered by water (condensate).

·     The heating process will be slowed down. As a result of the increase in the quantity of water in the autoclave, the load volume increases. Under normal conditions, the load in the autoclave is the AAC block. However, if the amount of water increases, the load represents the combined masses of water + AAC block. Consequently, as the load volume increases, more energy is required to heat the autoclave. However, since the energy supply (which is a function of pipe diameter, steam boiler, steam pressure and steam flow rate) is designed only for AAC blocks, increasing the load volume will cause a reduction in the heating rate.

·     The temperature is reduced. The energy transfer between water and steam is faster than that between AAC block and steam. A higher quantity of condensate therefore results in faster energy transfer. This in turn is related to a loss in pressure, for reasons discussed above. And finally, a loss in pressure results in a lower temperature, since there is a balanced relationship between temperature and steam pressure.

If the hot steam, which has a temperature of around 192°C, is in the upper part of the autoclave body while the water, which has a temperature of less than 100°C, sits in the lower part of the body, the resulting difference in temperature between lower and upper body volume can blow the autoclave door off and the whole autoclave can explode.

Fig. 3 and 4 show the deformation, yellowness and depressions on the product surfaces caused by inadequate autoclave design, faulty operation and condensate formation.

Maintenance of autoclaves

In AAC plants there are usually several autoclaves in operation and each autoclave is operated in different time periods according to the system requirements. In addition, the autoclave does not work alone and must be integrated with other production sections. The software to be used on the system has to therefore be prepared under consideration of the factors related to processes, operators and safety. In the Kotsa-AAC Software, all autoclaves work fully integrated with other systems. This allows innovations such as automatically determining the following aspects:

·     Best autoclave to start.

·     Best autoclave to transfer.

·     Best autoclave to pause during any unforeseen fault.

·     Lead operator during any fault.

·     The number of autoclaves that can operate, based on the operating time of the steam boiler.

·     Forecast of the estimated curing duration.

The system not only prevents operator mistakes, but also guides the operator towards easy and smart use.

The software allows the operator to select between automatic, semi-automatic and manual modes and has also taken product safety into consideration, accounting for any problems that may arise due to internal or external reasons.

In addition to all of the above-mentioned advantages of the Kotsa-AAC software, the maintenance module of the software is also special. Maintenance is a measure of maintaining the target condition and may involve minor work on the equipment, thus delaying or preventing wear. In the process, it therefore ensures an operational extension of the service life of the entire plant. Consequently, maintenance is of great importance for the overall condition of the plant. Maintenance works include the following aspects:

·     Cleaning.

·     Review of plant components.

·     Carrying out a test run.

The Kotsa-AAC software provides a reliable maintenance card which includes all necessary information and logs all performance data. The log serves as proof when it comes to warranty claims or the resale of a plant. How often maintenance is necessary depends on numerous different factors. The maintenance interval should therefore be determined individually for each object or system. Fig. 5 shows an example of a maintenance card.

Transfer system

Due to the large number of autoclaves in AAC plants, steam transfer (steam transfer from autoclave to autoclave) is very useful and not only reduces the cost of steam, but also provides great benefits for the carbon footprint of the product, which is an important issue to consider nowadays. While the transfer process is not used by all systems, some systems make use of manual operations. The Kotsa-AAC software recommends the first and second transfer options to the operator, considering multiple factors. Consequently, approx. 40-50% of the steam is recovered in the first transfer, and a proposal for the second transfer is made taking into account production schedules and shift hours. Transfers are recommended at the beginning and the end of the process.

Based on many years of experience, Kotsa provides engineering services related to software, commissioning and process-based commissioning/renewal of new and/or old machines for AAC production systems. The company has already demonstrated its expertise in the AAC industry in the field of engineering services and installation twice in the last three years.