Jacketed heating is a commonly used system for heating food processing devices such as tanks, kettles, dryers and reactors up to temperatures of 350°F.
Steam heating is often the first option considered by designers in these applications. It is readily available, easy to apply, predictable and provides quick heat-up.
Despite these advantages, steam presents several problems for jacketed heating applications by not offering precise temperature control.
Further issues are caused by the transfer of energy not being uniform, commonly resulting in hot spots. Hot spots around the jacket increase the likelihood of product burn-on and local overheating.
Reactions requiring both heating and cooling present other complications. Contact between the hot steam and the cool water can cause thermal shock and steam hammer that could be catastrophic for glass-lined reactors. At the conclusion of the heating cycle, all steam and condensate must first be driven out of the jacket before cooling water can be added.
Hot water: a better choice for jacketed heating applications
As a result of these disadvantages, many system designers are switching from steam to hot water for their jacketed heating applications. Operating temperatures can exceed water’s sea-level boiling point of 212°F if the water is pressurised.
Hot water heating solves some of the problems caused by steam. The temperature in the jacket can be controlled much more accurately. This ensures a better-quality end product and protects against damage from overheating.
This method allows smooth transitions from heating to cooling with no thermal shock or steam hammer, providing protection for glass-lined reactors.
Hot water distributes heat more evenly than steam, eliminating hot spots.
It is also environmentally safe and nonflammable.
There are a few downsides to hot water heating. The heat-up time is not as rapid when compared to steam. In addition, the jacket water temperature cannot equal or exceed the saturated temperature of the steam supplied to the system to prevent the water flashing back into steam.
Direct Steam Injection for jacketed heating
Steam still has an important role to play in jacketed heating. A Direct Steam Injection (DSI) heater provides the most precise and energy-efficient method for heating the jacket water to the desired temperature.
The DSI system operates by injecting steam directly into the water for an efficient transfer of heat. 100% of the available energy from the steam is instantly absorbed by the liquid.
The large amount of energy available in the steam makes it imperative that the energy is dissipated quickly into the fluid to maintain stability. The Pick DSI Heater accomplishes this by dispersing the steam in many fine streams through precisely arranged orifices for rapid mixing and instantaneous heat transfer.
As the steam enters the internal injection tube, it acts against a spring-loaded piston to expose some or all of the patterns formed by the orifices. As the steam input varies due to load changes, the piston modulates to adjust the number of exposed orifices, providing rapid response to process changes.
The spring-and-piston arrangement prevents equalisation of steam and liquid pressures, eliminating harmful shock and vibration. The helical flights inside the chamber ensure complete and thorough mixing of steam and liquid.
DSI Advantages in jacketed heating applications
DSI offers precise temperature control within ±1°C.
The process can be adjusted to any predetermined rate. DSI can easily accommodate cascade controls, allowing heat as well as heat-and-cool applications.
DSI is easy to install and can be used wherever medium to high-pressure steam is available.
Compared to alternatives such as tank steam sparging or indirect heat exchangers, DSI’s efficient heat transfer can cut fuel costs by up to 28%.
DSI is compact and quiet. The Pick DSI operates at a noise level below 85 dBA, far lower than other systems. It also features a low liquid-side pressure drop, less than 2 PSI, reducing unnecessary additional pump head pressure.
The system has low maintenance costs. Pick Heaters have only one moving part that can be easily inspected. It is also inexpensive to replace.
Unlike heat transfer fluids, which require special handling and constant monitoring, DSI is environmentally safe and non-flammable.
Many industries take advantage of jacketed heating and DSI.
The food industry commonly uses jacketed kettles to heat scorch-sensitive products such as beverages, soups and sauces. A DSI heater controls the jacket temperature to ±1°C, eliminating the risk of heat-related spoilage from burn-on.
The chemical and pharmaceutical processing industries also rely on jacketed heating for viscosity reduction in heavy liquids and precise heat to begin exothermic reactions.
Pick Heaters for jacketed heating
Water is superior to steam for heating jacketed reactors because it eliminates hot spots and uneven heating, allowing smooth transitions from heating to cooling with no thermal shock. DSI is superior to other methods for heating water due to its responsiveness, accurate temperature control and economical operation.
