The heating of fibrous, mineral or viscous slurries has long been among the most challenging heating applications in fluid heating. Although using steam sparging nozzles for slurry tank heating is the industry standard — plugging, fouling, and inconsistent heating make conventional indirect heat exchangers impractical in most cases. Therefore, direct steam injection (DSI) is often selected for these complex applications because of its temperature control, reduced maintenance, energy efficiency, and general ease of use compared to indirect heating methods.
Disadvantages of Spargers
In a sparger, the steam is directed from a central source to an array of holes. An external steam valve controls the amount of steam flow injected into the fluid. This modulating control valve -lessens the pressure of the steam in the sparger, reducing the flow of steam into the fluid heating process.
Poor Tank Temperature Control
By injecting the steam at the bottom of the tank, there is a risk of inconsistent temperature throughout. This is because most heat will be absorbed in the bottom, and much less heat will reach the surface. Therefore, uneven steam mixing and heat transfer can lead to product inconsistency and wasted energy.
When steam is not mixed thoroughly, steam bubbles can collect and form into larger bubbles. When the large steam bubbles encounter the tank, they will rapidly condense. As a result, cavitation will eat away the steel walls, and the tank will eventually start to leak. Damage to the tank from steam cavitation is widespread at most sludge heating facilities. It can result in high maintenance costs or, in some cases, the need to replace the tank altogether.
Lack of Steam Condensation
Steam may potentially face issues condensing into the slurry and go right through the tank and out into the atmosphere. This increases energy costs since the energy used is being wasted
Advantages of Heating with Hydro-Thermal's DSI Solutions
Accurate Temperature Control
When using a Hydroheater for slurry tank heating, all the slurry will enter the tank at the correct temperature, causing minimal temperature stratification across the tank.
Keeping all the steam injection contained at one point will prevent damage to the tank from sparging. In addition, it will reduce the number of maintenance hours required for fixing the slurry tank.
All steam will be condensed in the Hydroheater before it is discharged into the slurry tank, and no steam will be lost to the atmosphere. This will reduce the amount of steam needed for the exact temperature rise, and there will be lower fuel usage at the boiler.
DSI has become the standard for most slurry heating installations for consistent and reliable heat transfer and trouble-free operation. These devices utilize internal control of steam through a constant pressure choked flow nozzle/ plug arrangement. This plug/nozzle combination provides consistent, high-velocity steam throughout its full heating range. In addition, the high-velocity steam present in the heaters and the lack of hot product contact surfaces prevent the build-up of product inside the heater. This ensures consistent performance throughout its life.