Tuesday, November 20, 2012

Manufacturing of Di Calcium Phosphate(DCP)

         Di Calcium Phosphate is the by product of ossein manufacturing.  Crushed bone contains both inorganic and organic part.  In acidulation process the inorganic particles like calcium and phosphate dissolve in hydrochloric acid and form monocalcium phosphate (MCP).  MCP is converted into DCP in DCP Plant.  MCP is converted into DCP by reacting with lime.  Chemical formula of DCP is 2 (CaHPO4 2H2O).  DCP is marketed in powder form and is used in poultry feed. 

DCP Production 

In acidulation reaction in acid bath tri calcium phosphate react with Hydrochloric acid and mono calcium phosphate is formed according to the reaction.
          Ca3(PO4) + 4 HCl           =    Ca(H2PO4) + 2CaCl2       
            MCP from storage tank is pumped to the reaction tank in DCP plant.  In reaction tank lime is added and MCP is converted into di calcium phosphate.  

Lime Preparation

Lime slurry from lime mixing tank is pumped to the lime tank in DCP plant.  Fresh water is pumped to the lime tank.  By adding fresh water Baume of lime slurry is reduced to 5.0.  This lime is pumped to the DCP reaction tank.  In lime and water mixing tanks agitators are used for proper mixing.

DCP Reaction Tanks

          DCP plant consist of five reaction tanks named as H1, H2, H3, H4 and H5.  There are two DCP pumping lines in a reaction tank.  There are lines for pumping lime slurry and water.  Reaction tank is equipped with agitator for through mixing of reactants.  Capacity of reaction tank is about 140 m3.
DCP Plant Details
          DCP plant consists of 9 tanks.  Out of which five are DCP reaction tanks.  Two tanks are called separation tanks which are used for storing DCP slurry.  Remaining tanks are used for lime slurry preparation and collection of overflow from the filter containing slurry mixture.  DCP plant consists of vacuum drum, filter, HTV unit, bag filter and storage bins.

DCP Formation

          MCP is pumped to the reaction tank up to ¾th of the reaction tank volume.  Lime is added from the lime storage tank. Lime slurry Baume should be always maintained at 5.0.  Before adding lime pH of MCP is tested using pH meter.  If it is less than 2.0 some back slurry from DCP reaction tank is pumped to increase the pH.  pH of reaction mixture is checked in every hours.
Standard pH values.
          MCP (Before adding line)        2.0 - 2.4

          After 1 hour                            3 – 3.4  
          After 2 hours                           4.3 – 4.7
          After 3 hours                           4.9 – 5.1
          After 4 hours                           5.5 – 5.7
          Just before settling                            5.6 – 5.8
          MCP is fed continuously in to the reaction tank till it reaches a height of 1.5 m to 2m from the lop.  After this MCP and lime slurry is pumped together for one hour.  After one hour pH reaches to 3.2 then MCP pumping is stopped and reaction is controlled by adding lime alone.  After 3 hours of reaction when the pH is near to 5.0, addition of lime is reduced and added drop wise.  When pH value reaches 5.6 lime addition is stopped and agitation is continued for one hour.  After this reaction mixture is allowed to settle.  Settling process takes about one and half hour.
          A special type of powder, corrofloc is added in the form of slurry to reduce the settling time.
          The top portion will contain CaCl2 and unreacted MCP.   This liquid is siphoned to the effluent plant.  Syphoning process take about 2 hours.  After siphoning fresh water is added and agitator is started.  Water washing is done to remove impurities present in the slurry.  The slurry is allowed to settle for one hour and water is siphoned.  The pure slurry is pumped to the separating tank, from there it is pumped to the filtration unit for filtration using rotary vacuum drum filter.
DCP Filtration
          DCP slurry is pumped to separation tank using centrifugal slurry pump.  When the reaction tank becomes almost empty, tank is washed using fresh water.  This water also pumps to separation tank.  In separation tank well agitation is provided.  There are two separation tanks in the plant. 
For filtration slurry from the separation tank is pumped to a vacuum filter.  In this unit, a vacuum pump, a filtrate pump and a rotary drum are used for filtration.
          Slurry from separation tank is pumped to the drum filter through a valve for controlling the flow.  Water is also pumped in to that region for mixing up of solidified DCP into slurry.  This slurry is filtered using a vacuum drum filter in DCP manufacturing section connected to each separation tank.
For filtration slurry from the separation tank is pumped to a vacuum filter.  In this unit, a vacuum pump, a filtrate pump and a rotary drum are used for filtration.

             Vacuum drum filter is a large perforated drum rotating on its axis with slow r.p.m.  The drum is divided into three compartments.  Vacuum is reached in each compartment with the help of high flow valve.  A filter cloth covers the outer surface of the drum.  When the drum is rotating on its axis, one of the three compartment of the drum makes in contact with the slurry.  The vacuum is applied to the portion of drum which is submerged in the slurry through a high flow valve.  The liquid is sucked into the compartment and the moisture content of the cake is again reduced to a lower value.  At the next time vacuum is released and the cake falls down from the filter cloth to the chute.
          The filter cloth is washed in acid water after 3 or 4 uses.  There is a tank situated at the bottom of the drum filter for collecting the balance water from the drying side and it is recycled into the drum filter for diluting the DCP slurry in slurry tank.  In the filter the vacuum sucks the air and water from the drum filter through two pipes.  Air is sucked to the outside and one small portion of the water is pumped to the collecting tank at the bottom of the drum.  Vacuum pump is used for sucking air and water.

The wet DCP cake contains moisture of about 30% falls into a vibrator and a crusher.  This powder is subjected to fluidized bed drying.  The hot air required for DCP drying is provided by HTV 750.  Hot air is given from bottom and DCP particles travel against the hot air and gets dried.  The upper movement is caused by the suction of blower called J-10 blower.  Moisture content of DCP is reduced to 5%.

          Two thermo couples are provided one at the upper part of the crusher and another at the bag filter side.  When the thermo couples shows a reading of 60 then there is an increase of slurry feeding at the drum filter and filter goes shut off.  Normally the range for this purpose is 80-1000C.   If the second thermocouple provided at the bag filter shows a reading above 100, then a valve is opened and fresh air blows into the passage of DCP.  If powder gets high temperature and this causes some problems for the bags provided in the bag filter.  At this time the slurry feeding is also increased.        
          Hot air and DCP mixture enter to a bag filter, air inside the bags sucked by J-10 blower and DCP particles deposit over the bag.  144 bags are used in each bag filter.  The plant consist of two bag filter units.  There is one open end for bag.  All the open ends of the bags are connected in to a common open and sucks the air inside the bags by a J-10 blower.  To remove the deposited solids air hammering is applied at the regular intervals of 12 seconds.  The compressed air jet is given at the inside of the bags and the DCP deposited falls on the bottom.  Mechanical hammering is also applied to the side of the filter to remove particles stick to the side plates.
          Base of bag filter is equipped with a screw conveyor.  Discharge from screw conveyor section is passed through a rotary valve to prevent the suction of J-10 blower.  The DCP is then conveyed through pneumatic conveying to storage bin and the air in the bin also sucked to outside of plant.  At the bottom of bin an auto packing arrangement is provided.  It packs 50 kg of DCP in to bags. 

Important things to be noted in DCP reaction

1.       MCP pH should not go too low
2.       Lime concentration should be checked in certain intervals, other wise reaction schedule will not match with standard results. 
3.       During siphoning, siphon fixing is very important.
4.       Reaction should be started only after getting standard pH.
5.       The hourly reading of DCP reaction should be matched with standard values. 

Important things to be noted in DCP drying 

1.       Drum should be operated with constant speed with constant slurry feeding.
2.       Through should not get overflowed.
3.       HTV temperature should not go lower than 2000C.
4.       If cloth adherents is very low, cloth to be changed immediately.
5.       Filter cloth must be washed in acid water after 3 or 4 uses.
6.       Bag filter to be checked in periodic intervals.
7.       The temperature of DCP particles to the bag filter does not increase above 1000C.
8.       At the time of power failure or other break down all lines connected to filtration should be washed with water to avoid choking.
           In DCP packing DCP is packed in HDPE bags using auto packing arrangements.  Bags per pack are 50.4 Kg.  It is transported to storage by belt conveyor and stored.  A number of blowers are used to avoid dust particles. 

DCP Specification

          Moisture by weight                 :         5% Max.
          Phosphorous (P) by weight     :         7% Min
          Calcium                                   :         22.5 Min
          Flurine                                     :         0.2% Max.
          Acid Insoluble                         :         1% Max
          Particle Size by weight            :         90% through 100 mesh
          Colour                                     :         Near white 





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