Direct steam heated vaporizers are similar in appearance to the direct water heated vaporizers but offer higher vaporizing efficiency per unit of surface area. Performance is relative to the available water temperature.

They are extremely simple to operate. The VSU series vaporizer is normally used as a stand-alone vaporizer where the customer provides good quality clean steam, usually form a generator or process stream. The vaporizer is able to operate in either vertical or horizontal configuration. Capacity is dependent upon shell side steam temperatures. Direct steam circulating vaporizers are not really suitable for processes where the gas outlet temperature is sensitive and must not be elevated going to the process. When steam is used as the vaporizing medium there is a risk that when the cryogen flow is reduced or the control loop lag is such that there is a delay in the reduction of the steam flow rate, elevated gas outlet temperatures result. The VSU, however, is ideal for constant flow rate processes and represents the most economic solution to high volume flow rate applications. 

It represents the ultimate, reliable, cost effective, economic solution for simple gas vaporization. The vaporizer is designed such that the flow rate of the available steam is matched to the required maximum vaporization heat load. This ensures full vaporization of the incoming cryogen with an acceptable gas outlet temperature. The steam flow rate becomes a fixed parameter drastically simplifying the controls necessary to operate the vaporizer. If the cryogen flow diminishes full vaporization is still achieved, but the gas outlet temperature approaches closer to the steam temperature, which may be undesirable. In this mode of operation the vaporizer “self controls� requiring only a minimum of additional simple controls. A fixed steam flow rate also avoids other operational problems. A serious consequence of reduced steam flow, other than reduced capacity, is the potential freezing of the water onto the tubes. If this occurs the possibility of serious ice build up in the vaporizer boiling zone is present. As the ice builds it fills the spaces between the tubes, and if it continues unabated, damage to the tubes is inevitable. Although the damage is only local it will render the vaporizer inoperable. This problem worsens with decreasing water temperature, and any operating temperatures outside the normal design parameters should be reviewed by Cryoquip applications engineers.

Individual heat exchangers are commonly used as a local product vaporizer, and also for disposal vaporizers for air plants. They can be utilized as part of a large back up system, these units are frequently used in back-up service.

A basic standard pressure steam control package is included in individual steam heated vaporizers. Higher pressure steam controls are available as an option. A standard safety system option is also available.