Improving and maintaining the performance of your Heat Exchanger or Condenser.
The usage of Heat Exchangers or Condensers is common in many processes across a wide range of industries. The Energy sector is no different, either in the Thermal Power Generation, Upstream and Downstream of the Oil and Gas including Petrochemical and Chemical plants; Heat Exchangers are used to cool of the steam or to pre-heat different liquid needed in the processes. The recurrent problem of micro-fouling and scaling in heat exchangers and condenser tubes reduces plant output, performance and service life, when using raw water or recycle water in the cooling system.
During the heat transfer such material precipitate out of the circulating water and form scale and bio-fouling over the tube surface. This formation will act as insulation layer against heat transfer, reduces heat recovery, reduces process efficiency, reduces through put, reduces plant availability, while increasing plant operating and maintenance cost.
It is common practice for the heat exchanger and condenser manufacturer to design them with a “Fouling and Scaling factor” which translate in a larger unit to increase the running time before requiring a cleaning service or redundancy (standby) of several units to be able to service the fouling unit offline without losing capacity.
There are typically two approaches in cleaning and maintaining the heat exchangers/condensers; Offline and Online, both have several methods or technologies, with advantages and disadvantages
The most used in the offline approach is what is called “Pigging” where a bullet-like device is put in each tube and forced down the tube by high pressure air, other methods such as Hydro-Blasting, Hydro-Lancing or Chemical clean are also common practice in off-line cleaning.
After each off-line cleaning, the exchanger/condenser starts to operate at its high and designed efficiency and heat transfer rate. However, shortly after the operation begins the scale and fouling starts to slowly build up again and the performance of the heat exchanger deteriorates. Plant engineers’ challenge will be to balance the frequency and number of cleaning cycle VS. the loss/gain in the efficiency, and interruption in plant operational production.
This method of preventing scaling and biological fouling requires no shut down of the heat exchanger, or interruption of plant operation. When used alone or in conjunction with some chemical treatment, On-line cleaning will prevent the reduction in the heat transfer rate, maintain the tubes cleanliness factor at its clean condition, increase tube life, increase heat exchanger efficiency, reduce operating costs, and eliminate heat exchanger shut down (Fig.1)
Fig.1 Condenser Cleanliness Factor Vs. Time
Two type of on-line cleaning system have been used at different thermal power generation as well as refinery and petrochemical facilities around the world. They include the Brush and Basket type and the re-circulating Ball type system
BRUSH & BASKET SYSTEM
The system consists of a single Automatic Flow Diverter Valve, installed between the inlet and the outlet of the heat exchanger. The flow Diverter provides for periodical automatic back flushing/flow reversal through the heat exchanger while the exchanger remains in full operation with full flow through the unit. The diverter valve returns the flow to the “normal” direction after a few minutes (Fig.2).
Source: WSA Engineered Systems
Fig.2 Flow Diverter at heat Exchanger inlet in Normal & Reverse Position
Each heat exchanger tube will include a set of two baskets, one mounted at each end of each tube, and one brush in each tube. The steel baskets are located at the end of each tube by means of a false/secondary tube sheet mounted against the exchanger’s tube sheet. This allows full access to the tube bundle by unbolting the secondary tube sheet (Fig.3).
Source: WSA Engineered Systems
Fig.3 Installation of Brush and Basket sets inside the Exchanger
The brush movement through the tubes relies on the reversal/back flushing of the fluid through the heat exchanger, which is accomplished by the flow diverter valve installed at the heat exchanger. Each time the flow is reversed the brush located in the basket on the far end of the tube is propelled through the tubes removing any build up growth tube wall. Moments later the flow is put back to its normal position and the brushes are once again shuttled through the tubes.
Each reversal cycle only lasts a few minutes, the reversing of fluid and shuttling of the brush is done as many times per day as necessary, depending on the type of fluid flowing through the exchanger and the extent of scale and fouling formation. The flow reversal and brush shuttling does not interfere with the exchanger or the process operation (Fig.4).
Source: WSA Engineered Systems
Fig.4 Installed Flow Diverter at the Exchanger
Recirculation Ball System
The operation of the Ball System is based on the circulation of the elastomeric, slightly oversized rubber balls through the heat exchanger tubes. The balls are periodically or continuously injected into the heat exchanger inlet line and are re-circulated through the heat exchanger tubes by the water flow. Because the balls OD is slightly larger than the tube ID, the tubes are automatically kept clean by the scrubbing and wiping action of the balls, which prevents the buildup of the deposits inside the tube surfaces (Fig.5).
Fig.5 Typical Balls
The balls are collected by a screen housed within a spool pieced strainer which is located at the water discharge pipe from the heat exchanger. After balls are collected they are removed from the strainer by means of a pump and are passed through a collection vessel before they are re-injected back into the heat exchanger inlet line (Fig.6)
Fig.6 Typical Strainer installation and Ball removal/reinjection
The externally located ball collector vessel located on the ball re-circulation pump skid is used to remove and replace or add new balls when needed, without any needs for system shut down. The system is fully automated and controlled by the plant DCS or locally mounted Control Panel (Fig.7)
Fig.7 Typical installed System
Choosing a system
Both system are considered effective and are used within the Energy section applications. The selection is site specific and much depends on the heat exchanger; process and operating condition.
On-Line Automatic Tube Cleaning System has been proven to be an effective and most economical method to keep heat exchanger and condenser tubes clean and at their top performance.
- Automatic Tube Cleaning Systems work 24/7 to eliminate the build-up of any deposits, reducing the frequency of costly maintenance shutdowns while optimizing equipment function.
- Removing scale from heat exchangers and condenser tubes is costly and labor-intensive.
- The productivity lost during such downtime can never be recovered. The Brackett Green® automatic tube cleaning system (ATCS) eliminates maintenance costs associated with chemical/offline cleaning.
- By injecting appropriately sized elastomer balls into the tubes, the ATCS wipes them clean of deposits. This simple system improves plant performance; increases service life and minimize maintenance costs.
For more information Ovivo.Energy@ovivowater.com