Q&As about POMEVap

Q: How do you recover oil from a solid concentrate produced by the Alfa Laval POMEVapPlus system? Assuming the POME contains about 1% oil, how much oil can be recovered?

A: The oil content in the raw POME is typically 0.5% to 1% by weight. The raw POME is concentrated in the POMEVapPlus system and, due to this concentration process, the oil content in the solid concentrate increases severalfold. The concentrate with higher oil content is fed to an Alfa Laval PANX decanter, which is integrated into the POMEVapPlus system. The PANX decanter helps recover the oil from the solid concentrate. About 50% of the oil present in the raw POME can be recovered using POMEVapPlus system.

Q: It is mentioned that the POMEVap or POMEVapPlus solution can be implemented in new mills as well as in existing mills. In both these cases, what considerations one should take into account? Can POMEVap/POMEVapPlus operate if the mill is not operating at its designed capacity?

A: The POMEVap and POMEVapPlus solutions are highly flexible and Alfa Laval can therefore implement these solutions in existing mills as well as in new mills.

In some existing mills, the available steam and electric power is limited; therefore, we need to analyze and decide on the number of effects in the POMEVap to match the steam and electric power available on site. The mill can also investigate the possibility of running the mill boiler and mill turbine at the maximum possible capacity by using available surplus biomass on site. This provides additional steam and power that can be used in the POMEVap system. Running the POMEVap system requires that the system receives steam and electric power from the mill as per the design utility data.  

In the case of new mills, it is best to design the POMEVap during the conceptual design phase of the mill. The mill boiler and turbine capacity must be appropriately sized to meet the steam and power requirements of the POMEVap system.   

Q: With the SteamVap system, it is possible to generate the steam using separated water from POME in the POMEVap system. Can the SteamVap system help improve the efficiency of the mill boiler?

A: The SteamVap system can improve the efficiency of the mill boiler through efficient condensate recovery. In the existing mills, the steam from mill boiler is used in the sterilizer unit to sterilize Fresh Fruit Bunches (FFBs) through direct steam injection. Upon contact with the FFBs, the steam is converted into dirty condensate (POME), which is then sent to the sludge pit for treatment. This represents loss of condensate in the form of POME. The loss of condensate therefore represents loss in boiler house efficiency.

However, with the SteamVap system, it is possible to convert the separated water produced from POMEVap into steam and use the steam generated to sterilize the FFBs. The dirty condensate from sterilizer is again processed in POMEVap, and clear water is produced; this is used once again in the SteamVap to produce steam – and this cycle continues. To generate steam, the SteamVap system utilizes the steam from mill boiler. The SteamVap system utilizes the mill boiler steam and produces clean condensate which can be then recirculated and reused in the mill boiler house, thereby improving the boiler house efficiency.

Q: What is the quality of the oil recovered by the POMEVapPlus system?

A: If the fresh raw POME is processed (without too much delay) in POMEVap, then the oil recovered is similar in quality to the oil recovered in the oil room. The recovered oil in the POMEVapPlus system therefore can be returned to the clarification section of the mill for purification.  

Q: Is it possible to use an energy source other than steam (for example, flue gas from boiler) in the POMEVap system?

A: The turbine exhaust steam is the preferred energy source for the POMEVap since it is available as ‘free’ steam and can be easily distributed and transported from the mill boiler to the POMEVap system.

The other possible energy source is electric power. The POMEVap based on Mechanical Vapour Recompression (MVR) can be used if the mill can supply the required electric power.

The direct use of flue gas is not recommended due to practical issues such as routing the flue gas ducts from the mill boiler to the POMEVap system. The waste heat from flue gas can be transferred to the water, and the hot water generated can be used as an energy source in the POMEVap system. However, the available heat in the flue gas and the temperature of hot water generated needs to be carefully analyzed before making any decision about using flue gas as an energy source.     

Q: How does the POMEVap system perform with regard to fouling? How often does the POMEVap system require cleaning?

A: The POMEVap system is based on Alfa Laval AlfaFlash technology, which is a forced circulation plate evaporator. The AlfaFlash evaporators use carefully designed liquid recirculation flows to create the necessary shear rates and turbulence inside the channel plates of the heat exchangers. This, in turn, helps minimize fouling and maximize uptime. With a stable feed supply and utility supply, the POMEVap system can run continuously for several days. After stopping POMEVap operation, a single hot water cleaning cycle is sufficient to clean the system efficiently. Periodic caustic cleaning is also recommended to achieve better cleaning efficiency.

Q: What is the most economical configuration of the POMEVap system? Is it a triple-effect POMEVap system or a four-effect POMEVap system?

A: The optimal and most economical configuration of the POMEVap system is based on analysis of both capital investment and operating costs. The higher the number of effects, the lower the operating costs due to lower steam consumption but higher capital investment costs. On the other hand, designing a POMEVap system with fewer effects reduces the capital investment costs but raises operating costs due to higher steam consumption. The number of effects is therefore a trade-off between capital expenditures and operating costs. If steam availability in the mill is limited, then choosing a higher number of effects (perhaps five or six effects) is necessary in order to match the steam available on site.

Q: Do we need to treat the process condensate from the POMEVap system for use as feed water in the SteamVap system?

A: We only adjust the pH value of process condensate to 7.0 before feeding it to the SteamVap system. There is no need for additional treatment of the process condensate since the SteamVap can easily handle the quality of process condensate.

Q: Instead of having a common POMEVap system, is it possible to install a POMEVap for each POME generation point (sterilizer section or clarification section)?

A: Yes, it is possible to install POMEVap for each POME generation point (sterilizer section or clarification section). However, installing a single POMEVap system simplifies operations, making operations more efficient, cutting installation costs and reducing the number of staff needed to operate the system.

Q: Must the existing boiler capacity be upgraded in order to provide the steam required by the POMEVap?

A: If the mill turbine is producing more power than required to operate the mill, then there will be surplus turbine exhaust steam available in the mill. This surplus steam can be supplied to the POMEVap system. If the available exhaust steam is less than what the POMEVap requires, then the mill can investigate the possibility of running the mill boiler and mill turbine at the maximum possible capacity using available surplus biomass on site to produce more power and more exhaust steam from mill turbine, which can be then supplied to the POMEVap system.