The main purpose of DM+UF plant is to supply de-mineralized water to various systems with the priority to provide for steam water system for producing steam to run the turbine. The water from the plant will also be used as jacket water of diesel generators, air compressors and chillers.
The process employed for DM+UF plant is the simple ion-exchange method with cat ion bed, anion bed and mixed bed.
The capacity of the Plant is 48m3 per stream for outlet and inlet is 56m3 per stream.
The Plant employs several chemical and physical processes to de-mineralized water namely.
1. Dual Media Filter (DMF) - This process is also called Pressurized Sand Filter as larger suspended impurities and organic matter are removed in this process.
2. Activated Charcoal Filter (ACF) – This process strictly removes chlorine from inlet water as presence of chlorine may chemically damage the cation resin present in the bed.
3. Strongly Acidic Cation Bed (SAC) – The main purpose of strongly acidic cation bed is removal of cation from inlet water.
4. De-Gasser Tank – This particular tank is used for removal of carbon dioxide as carbon dioxide presence may cause unnecessary load to the anion bed.
5. Strongly Basic Anion Bed (SBA) – The purpose of this particular process is as the name suggests is to remove positively charged anions.
6. Mixed Bed (MB) – The SAC and SBA removes the cation and anion from the water but some amount of cation and anion resins are still distributed within the bed. The mixed bed is mainly polishing unit to refine the final outlet through SBA.
7. Ultra Filtration (UF) – This process of Ultra Filtration is a physical interaction only where no chemical reaction takes place to remove colloidal silica or non-reactive silica. UF modules are woven fiber filter which removes the non-reactive silica.
NB: There are two vessels for DMF, ACF, SBA and MB and three vessels for UF at the Plant Side.
The DM+UF Plant Panel have redundant PLCs, meaning that if one PLC goes to stop mode or shuts down due to any event or situation then the other PLC will take over ensuring the field input and output are unaffected from the one PLC shutdown. Similarly, even Ethernet Switches and Power Supply in the Panel are also redundant. The Ethernet switch used here also have probation of transfer of data from Fiber Optic Cable. The Ports 7 and 8 are for FO port whereas ports 1, 2, 3,4,5,6, are Ethernet Ports.
CYCLES IN THE PLANT
The DM+UF Plant can be divided into three sections each independent of each other. The following flowchart illustrates the section and their respective cycle.
SECTION 1: This particular section comprises of DMF, ACF and SAC each having two vessels from which either of the vessel can be selected for service or backwash cycle.DMF has three cycles namely Service Cycle, Backwash Cycle and Trip Cycle. There are further sub-cycles in Service and Backwash Cycle as defined by necessity of process requirements, each cycle results in operation of valves and pumps at the field. Similarly ACF and SAC have cycles of Service and Backwash with their further sub-cycles in each of the respective cycles.
SECTION 2: This section deals with SBA and MB having two vessels for each for the process with either of the vessels can be selected for Service or Regeneration Cycle. SBA has three cycles namely Service, Regeneration and Trip Cycle whereas; MB has only Service and Regeneration Cycle with each of the cycles having further sub-cycles except the trip cycle. The cycles results in valve and pump operations at the field.
SECTION 3: This section of UF has three vessels of which any two can be selected for Service cycle. The UF section has Chemical Cleaning Cycle and Backwash Cycle apart from service cycle. These cycles like the other two section also results in valve and pump operation at the field.
AUTOMATION SEQUENCE AT THE PLANT
The DM+UF is semi automated plant, the following flowchart illustrates the automation sequence of the plant.
NB: Section A, Section B and Section C cycle sequence is independent of each other.
DMF, ACF and SAC have two vessels each and each vessel has Auto and Manual mode. Service cycles require selection of any of the two vessels and their respective Auto mode of DMF, ACF and SAC. If there is any kind of fault or interlock issue at the plant then the whole cycle will trip in Section A. The other vessel of DMF, ACF and SAC can be taken in Manual Mode or Auto Mode for Backwash Cycle.
SBA and MB also have two vessels each and each vessel has Auto and Manual mode. Similar to DMF, ACF and SAC Service Cycle, even SBA and MB Service Cycle requires selection of any of the two vessels and their respective Auto Mode. The other vessel for SBA and MB can be taken in Manual Mode or Auto Mode for Regeneration Cycle. If there any kind of field Fault or interlock issue at SBA or MB then the cycle will trip in Section B when it is at Auto Mode. The Trip at SBA and MB will not affect other cycles at Section A or Section C.
UF have three vessels each having Auto and Manual mode. The Service Cycle at UF requires selection of two vessels and their respective Auto Mode. The other vessel can be taken in Manual Mode or Auto Mode for Chemical Cleaning or Auto Mode for Backwash. Fault or Interlock issue at UF section will only trip UF cycle and will not affect any other Cycles at the plant.
The Pumps have Auto and Manual Mode; the corresponding pump must be selected in Auto Mode in the required Cycles to run the cycle. It can also be operated without cycle operations when taken in Manual Mode. The Blowers, Valves, Pumps and Analog Inputs from the field has BYPASS probation included in the system, thus any of them are at fault then it can be bypassed from the cycles at Start Up or During Cycle without any intervention to the Actual Cycle Operation.