UltraFlex UltraFiltration Skids
CEB (Chemically Enhanced Backwash) vs CIP (Clean in Place)
There are two major methods of cleaning a membrane skid – Chemically Enhanced Backwash (CEB) and Clean in Place (CIP).
Filter Tech Systems’ UltraFlex process utilizes chemically enhanced backwashing (CEB) which prolongs the life of the membrane and eliminates the down-time required by other systems for their labor-intensive periodic CIP cleaning. Regular, automatic, daily chemical cleanings (CEB) with commercially-available cleaning compounds do not allow the material that causes fouling to collect on the membranes. The membranes are therefore more readily returned to their original condition.
Chemically Enhanced Backwashes are performed more frequently and on a regular basis. The goal is to keep the membranes from fouling rather than let them foul and then perform an extensive cleaning as is done with the CIP system.
The CEB Cycle is automatically performed after a certain number of hydraulic cleaning cycles. This cycle is fully automatic and requires NO operator involvement. The CEB process eliminates labor-intensive monthly cleaning cycles.
Cleaning volumes of chemicals are less with the Chemically Enhanced Backwash System. During the CEB cycle, cleaning chemicals are injected into the backwash stream and directly into the membrane module. During the CIP process chemicals must be mixed and the entire tank volume is filled with cleaning chemicals.
In the CIP process, cleaning chemicals are in open tanks and workers are exposed to potentially dangerous and unsafe working conditions. Chemicals could easily come in contact with skin and eyes. During the CEB process, chemicals are enclosed in piping from introduction to disposal.
Plants that use the CIP process operate the plant until the TMP (transmembrane pressure) is at its uppermost limit. This increases energy costs and also leads to shorter membrane life as the membranes are more fouled before cleaning takes place allowing the fouling particles to become more deeply embedded in the membrane fiber. This makes it harder to return to the original TMP which reduces the capacity of the membranes and shortens the membrane life.
The optimized performance gained by the Chemically Enhanced Backwash Process (CEB) reduces energy consumption, provides more stable operation and, most importantly, significantly lowers membrane stress and improves membrane life.
Low Flux Rates vs High Flux Rates
Membrane Equipment Manufacturers are faced with many forces which influence the design of their membrane skids. The major variable that affects skid design, capital costs and long-term operating and maintenance costs is the design flux rate.
Flux is defined as the volume of water pushed (pulled) through a given area in a given amount of time. In the membrane industry, flux is defined as gallons per square foot per day (gfd).
The goal of both Filter Tech Systems and Pentair/X-Flow when designing an UltraFiltration skid is low operating costs and ease of operation and maintenance. Of course, as a company, we must be sensitive to capital costs, but we try to look past that and design for the needs of the customer – to minimize operating time, keep chemical and electrical costs low and extend the life of the membrane as long as possible.
In general, skids designed with low flux rates are less sensitive to fouling and skids designed with high flux rates are more sensitive to fouling. Below are some comparisons:
Lower Flux Designs:
- Lower Flux Designs allow for more room for error in the event that the plant is hit with a fouling event (run off or storm event, high TOC or other raw water anomaly). The added membrane area (because of the lower flux rate) provides headroom for the plant to push through the fouling event while meeting capacity demands.
- Lower Flux Designs will often return to normal operation when a fouling event passes and without the need for more intensive cleanings.
- Lower Flux Designs are less likely to miss capacity demands due to lower cleaning requirements and difficulties. The skid will be off-line for less time over the life of the system.
- Lower Flux Designs have a tendency for lower TransMembrane Pressures (TMPs). Less pressure required to “push” (pull) the water through the membrane equates to lower energy costs.
- Lower Flux Designs reduce the cleaning frequency and thereby the cost of operation and chemicals.
- Lower Flux Designs lead to increased membrane life due to less chemical exposure because of less chemical cleanings
Higher Flux Designs:
- Higher Flux Designs are more sensitive to fouling events and it may be more difficult to work through the fouling event. More extensive cleanings may be required to return to normal operation.
- When Higher Flux Designs are hit by a fouling event they are more likely to fall short of meeting the capacity demands (due to additional backwashes and cleanings) and may require extended operator intervention until the system is restored to normal.
- Higher Flux Designs are more likely to miss capacity demands due to increased cleaning frequency and difficulties.
- Higher Flux Designs tend to have higher TransMembrane Pressures (TMPs) which result in higher energy costs.
- Higher Flux Designs require more frequent cleanings. This results is higher operating, chemical and electrical costs
- Higher Flux Designs lead to reduced membrane life due to the increased chemical exposure caused by more frequent or extended chemical cleanings
It is our goal (and our experience) that skids with lower flux rates are able to operate above the design flow rate, increase the time between hydraulic cleanings (backwash) and have less frequent chemical cleanings than skids with higher flux rates. Whereas winning the job is important, more important is a long-term successful installation that is simple to operate with low operating and maintenance costs.