Saturated vs. Superheated Steam in Laundry Plants: Problems and Solutions

During the laundry process, linen may quickly age. Heating may be slow. Uneven drying can appear during ironing. Workers often check water quality, equipment conditions, and operational procedures. If these sectors are normal, but problems still occur, check the steam quality. Steam temperature is not the higher, the better. The key to laundry and ironing processes is whether steam is saturated or not. Steam misuse can directly affect energy consumption, washing efficiency, linen lifespan, and delivery quality.

Differences Between Saturated and Superheated Steam

Saturated and superheated steam are used in different scenarios. For saturated steam, its pressure and temperature are related.

Saturated steam can quickly release a large amount of latent heat when exposed to cold. Its heat transfer efficiency is high. It is suitable for laundry and roller ironing heating. Laundry plants require saturated steam. Its temperature can be controlled stably via pressure. Heat can be released completely and controlled.

For superheated steam, its pressure and temperature do not correspond to each other. For example, when its pressure reaches 0.4 MPa, the temperature can exceed 180℃. Superheated steam is mainly used for power generation and long-distance pipe transmission. When it enters the heat transfer device, the temperature must be dropped to the saturated temperature at the corresponding pressure. This helps release more latent heat. A higher degree of superheat requires longer cooling time. This further reduces heat transfer efficiency. Thus, superheated steam is not suitable for linen washing and ironing.

On-site Assessment & Precise Inspection

Assess the steam trap venting and drainage state on site. The steam from the steam trap is nearly transparent, and the white vapor is invisible. It gradually appears after cooling further. Besides, the condensate amount is small. This may be superheated steam. Dense white vapor forms near the outlet, followed by a large amount of condensate. This is often saturated steam. However, this is a preliminary assessment. A slight superheat of 5–10°C cannot be discovered visually.

Precise inspection relies on pressure gauges and thermometers. Install pressure gauges at the back end of pressure-reducing valves and the inlet pipes of steam headers. This can measure the actual pressure. Then install platinum resistance temperature probes to measure the actual steam temperature. Check the standard saturated temperature at the current pressure based on the saturated steam table. If the actual temperature equals the table temperature, the steam is saturated. If the actual temperature exceeds the table temperature, the steam is superheated. The difference between the two is the degree of superheat. Do not rely on the pressure gauge to determine this. Superheated steam may occur at normal pressure. Throttling by pressure-reducing valves can cause steam to become superheated.

The Damage of Superheated Steam

If the degree of superheat often exceeds 20℃, the damage becomes obvious. During the laundry process, insufficient heating efficiency can cause linen to soak in the alkaline laundry solution longer. Thus, fibers may quickly age. Linen may become brittle and shed fibers. Also, this may reduce linen lifespan.

During ironing, roller temperature may be uneven. Localized superheating can cause linen scorching and yellowing. If the temperature is low, linen may still remain damp. Wrinkles can also appear. To improve drying performance, operators reduce ironer speed. However, this reduces production capacity as well as damages linen. Also, increasing steam pressure and temperature may worsen this condition. Synthetic fabrics and fine-count yarn linen are sensitive to temperature. Fabric sheen and stiffness can easily occur. This increases linen damage and compensation costs. If healthcare linen is not dried completely after ironing, bacteria can grow in damp conditions. This can also cause compliance risks.

A degree of superheat of 5–10℃ does not damage linen immediately, but can continuously increase energy consumption. Meanwhile, superheated steam can accelerate aging and damage of pipes, valves, gaskets, and seals. This can cause frequent spare part replacement and rising maintenance costs.

Adjustment Solutions

● Steam from factory’s boilers

Steam generated by boilers is often saturated steam. However, after long-distance pipe transmission, throttling, and pressure reduction, a slight superheat of 5–10℃ may occur when the steam reaches ironers or washers. For this slight superheat, optimize pipes and check pressure-reducing valves. This can avoid excessive superheating caused by throttling. Also, spray atomized softened water into the steam after pressure reduction. Water can absorb heat while evaporating. This removes excessive heat, reduces the degree of superheat, and forms nearly saturated steam. Thus, this meets the linen washing and ironing requirements.

● External steam source

Steam comes from power, chemical, and food processing plants. It may be superheated steam, and its superheat can reach tens of degrees Celsius. It cannot be used directly. Reduce its pressure and temperature via professional devices. Based on the working pressure, reduce the high-pressure steam to the required pressure. Then precisely spray qualified cooling water through an automatic system. The steam temperature should drop to the saturated temperature at the corresponding pressure. It can be discharged at a slight superheat state. The cooling water should be softened. This can prevent scale buildup and nozzle clogging.

Kingstar Case

Kingstar has a customer who has been operating a laundry plant for over 20 years. During the factory upgrade, it used Kingstar equipment, including tunnel washers and ironing lines. However, during the early stages of operations, the tunnel washer’s intake hoses often broke down. The customer questioned the component quality. Kingstar inspected the broken components. It confirmed that the components were not defective.

Kingstar’s after-sales and engineering teams immediately stepped in. Based on more than 20 years of on-site management experience, they checked the equipment installation, steam pressure, pipe layout, pressure reducing valve selection, steam trap conditions, and steam load. They did not simply attribute the problem to aging components and improper operations. They communicated repeatedly and tracked the operating data continuously. Also, they compared the findings with similar projects. After systematic troubleshooting and multiple inspections, they found the root cause: the plant directly used superheated steam from a power plant.

The steam pressure is normal, while its temperature is relatively higher. It seems to be more effective. However, superheated steam is not suitable for direct use. It should be cooled down to the saturated temperature at the corresponding pressure. Thus, it can release latent heat. If superheated steam always enters Kingstar tunnel washers, dryers, and ironing machines, this can accelerate the aging of intake hoses and seals. It can also reduce heat transfer efficiency. Uneven heating may also occur. This further affects washing efficiency and delivery quality.

Kingstar developed cooling and pressure-reducing solutions with customers. After implementation, steam met quality standards. The tunnel washer’s intake hoses no longer broke down. The heat transfer efficiency of dryers and ironing lines remained stable. Also, the linen washing efficiency and quality became consistent.

Kingstar team has accumulated years of on-site experience in the laundry industry. Also, it has systematic troubleshooting capabilities and offers customer-first services. Kingstar not only provides equipment but also helps them optimize equipment, processes, and energy systems. Thus, the factory can achieve stable, efficient, and sustainable operations, rather than relying on equipment upgrades. Also, laundry plants with similar issues can improve steam quality for washing efficiency and quality.

Conclusion

In linen processing, higher steam temperature may not offer better results. Superheated steam can reduce heat transfer efficiency, increase energy consumption, damage linen, and increase equipment maintenance costs. Laundry plants should check both pressure and temperature. Assess the steam quality and take targeted measures based on the steam from on-site boilers or external plants. Thus, steam can meet quality and temperature standards. Only by this can they improve laundry and ironing efficiency. Also, they can extend linen lifespan and reduce the risk of excessive energy consumption, repair, and compensation.

Q&A

Q1: What is the steam consumption of a Kingstar ironer?

A1: A Kingstar 650 series ironer consumes around 300 kg of steam when processing bed sheets per hour.

Q2: Can superheated steam be cooled by pressure reducing valves and steam headers?

A2: Simply using pressure reducing valves and steam headers cannot turn superheated steam into saturated steam. This can only generate throttle superheating. It may also increase superheating. Pressure reducing valves can only reduce pressure, not remove heat. For example, they can turn the saturated steam (164℃) at 0.6 MPa into 0.4 MPa. At this time, the steam becomes superheated.

Q3: What is the steam pressure for ironing bed sheets and duvet covers?

A3: The recommended steam pressure for a Kingstar ironer is 6 kg for duvet covers. Bed sheets require 2-3 kg of steam pressure. If steam pressure is insufficient, the processing speed should be slower.