Submerged combustion evaporators

This type includes solar pans and submerged combustion units. Submerged combustion evaporators can be used for applications where contamination of the solution by the products of combustion is acceptable. 

Ozark Mahoning A process for concentrating Wet process phosphoric acid by submerged combustion evaporation. Developed by the Ozark Mahoning Company and first installed in Pasadena, TX, in 1945. See also Nordac. 

Heating medium brought into direct contact with evaporating liquid (e.g., a submerged combustion evaporator)... 

The specialty evaporators make up the second classification of evaporator types. These are generally much smaller and simpler than the tubular evaporation systems, and are often batch or multipurpose evaporators. The third group is a unique classification and the direct-fired, submerged combustion evaporator is the best example of this type. 

Phosphoric acid concentrators may be classified as direct-fired or indirectly heated. In direct-fired evaporators, combustion gases come into direct contact with the acid, as in a spray tower or submerged combustion evaporators. Use of this type of evaporator has been abandoned because of the difficulty of cleaning the exhaust gases to recover acid mist and fluorine compounds,... 

Submerged combustion evaporators frequently are smaller than other types. They can be economically constructed entirely in corrosion-resisting materials. For this reason they are often used when evaporating highly corrosive fluids. 

Thermal efficiencies are high, ranging from 90 to 99% of the net heat input. However, since the vapor is mixed with large quantities of noncondensable gases, it is difficult to reusa the heat in this vapor. Sometimes the heat in the vapor can be used as a preheater or pre-evaporator before the submerged combustion unit. When the heat in the vapor cannot be recovered, low fuel costs greatly enhance the economics of the process. 

Figure 11-34 Evaporator vassals for submerged combustion evaporator.

In applications using heat transfer surfaces, when the submerged combustion unit is really only a heater, the water temperature must be below 140 F in order to avoid water makeup. These units normally operate such that the water from combustion exceeds the amount evaporated. 

The problems resulting from submerged combustion evaporation have been related to entrainment and stack emissions. 

There will be less use of evaporation schemes that inhibit the recovery of the latent heat energy of the vaporized water. For example, submerged combustion evaporation will be used only when absolutely necessary. 

Submerged combustion devices (SCDs) for a liquid heating and/or evaporation. 

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