1、N/C Metering system for urea plantsThe N/C value is one of the most important parameters to achieve an efficient production of good quality urea.NCpresentation SPIE2Stamicarbon and SPIEFor more than 20 years SPIE has been building N/C meters.Together with Stamicarbon the design is modified trough th

2、e years. NCpresentation SPIE3N/C Metering system for urea plantsWhy measure How measureLab analysisN/C MeterN/C meter designFunctionalityPressure reducerTemperature reducerMeasurementFlushingCoolingComponentsAngle valve & monoblockBack pressure regulatorFlushing installationN/C cabinet Auto flus

3、hStart-upShutdownTroubleshootingQuestions?Density tubeNCpresentation SPIE4Why measure?Control reactants at azeotropic ratio (to do so the, N/C ratio deviations must be as small as possible; the N/C ratio spread should be reduced !) NCpresentation SPIE5 Spread N/C ratio over a period of 24 hours- wit

4、h N/C meter control_ without N/C meter control324 HN/C changes due to difference in cooling water temp. during day and night. Stamicarbon: “We suspect this is mainly due to more CO2 being produced by the NH3 plant and the increased efficiency of the CO2 compressor at night”NCpresentation SPIE6Lab An

5、alyse:CarbamateUrea + water2 NH3 + 1 CO2CarbamateN/C = 2 urea + NH31 urea + CO2Measure WT%:UreaNH3Co2NCpresentation SPIE7N/C Meter MeasurementN/C = f (density, pressure, temperature)If pressure and temperature are controled and constant N/C = f(density)After research Stamicarbon discovered:NCpresent

6、ation SPIE8N/C ratio in the outlet of the reactorTemperature = 50 degPressure = 20 BargNCpresentation SPIE9N/C meter design criteriaSystem must include accurate density measurementSystem must provide and control stable temperature and pressure conditionsSolidification of urea must be prevented at al

7、l timesUndesirable conditions need to be indicatedGives a 4.20 mA output for N/C ratioNCpresentation SPIE10N/C meter connectionsABCreactorstripperc.w. air steamrectifying columnrecirculation heater flushing condensatec.w.steam drainN/C meterNCpresentation SPIE11Angle valve + monoblockCDABA combinati

8、on of two valves (angle valve & 3-way monoblock valve) for sampling, providing the possibility for isolation and flushing of the N/C metering system.NCpresentation SPIE12NCpresentation SPIE13Monoblock NCpresentation SPIE14Pneumatically actuated valveSteam tracingAngle valveMonoblock valveSample

9、INSample (or condensate) to N/C meterCondensate INTwo manual operated valvesProcess connectionNCpresentation SPIE15Flushing PumpCDABFlushing system to feed flushing water to the 3-way monoblock valve and the N/C meter.Automatically activated on flow, pressure, temperature alarm of urea sample.NCpres

10、entation SPIE16Flush pump headNCpresentation SPIE17Back pressure regulatorCDABBack pressure regulator (heated) for fine control of the pressure in the density transmitter. NCpresentation SPIE18BPR in detailNCpresentation SPIE19N/C cabinet (front side)CDABThe N/C meter cabinet with capillary pressure

11、 reducer, safety valve and density transducer.NCpresentation SPIE20Sample drainDensity meter & Sample flow meter and temperature (Trip alarm function)Cabinet temperature measurementSafety relief valveCapillary pressure reducer Condensate pressure swichSample Pressure transmitter Sample Temperatu

12、re Bleed valve密度計和取樣流量和溫度密度計和取樣流量和溫度柜內(nèi)溫度測量柜內(nèi)溫度測量取樣漏取樣漏樣品壓力變送器樣品壓力變送器樣品溫樣品溫度度安全泄放閥安全泄放閥毛細管減壓器毛細管減壓器冷凝壓力開關(guān)冷凝壓力開關(guān)泄放閥泄放閥NCpresentation SPIE21back-side N/C metering cabinetPressure switch cooling water circulationCooling water outletCooling water safety relieve valveCoolerCooling water inletL.P. steam in

13、letCooling water control valveCooling water pump循環(huán)冷卻水壓力開關(guān)循環(huán)冷卻水壓力開關(guān)冷卻水出口冷卻水出口冷卻水進水冷卻水進水冷卻水安全閥冷卻水安全閥冷卻器冷卻器冷卻水控制閥冷卻水控制閥蒸汽入口蒸汽入口冷卻水泵冷卻水泵NCpresentation SPIE22FlushingTrip alarmUrea temperature highUrea pressure highUrea flow lowStart flush pump (automatically or manual)Wait for the bleed valve to closeWa

14、it until flushing water pressure is higher than process.Monoblock valve opens and flushing starts.Flush the N/C meter until all conditions are typical.If the N/C meter does not work on water it will not work with sample.Stop flush pump by handNCpresentation SPIE23在線儀表在線儀表加熱箱加熱箱沖洗泵沖洗泵NCpresentation S

15、PIE24Start-up and shutdownAlways manual flushing.Make sure the sample line is clean and filled with water before shut down. After major maintenance flush for a long time.Do not put the N/C meter if the synthesis temperature is to low. Never put the N/C meter online if the flushing equipment is not s

16、tandby:Flush pump standbySteam condensate available at a temperature above 70CNCpresentation SPIE25TroubleshootingCapillary is blocked:FlushingHeat the capillary with steamMount capillary the other way Pressure is not constant:Check back pressure regulatorOpen regulator 100% and flush for 30 min.Rep

17、lace seat and seal of the back pressure regulatorSample temperature not ok:Cooling water temperature to highDelta pressure not big enoughCheck temperature controller (DCS)Check cooling water valveNCpresentation SPIEMaintenanceEvery Weekly:Start the flushing pump using pump test switch.Check steam pu

18、rge on the sample PSV.Check flow to the drain from the bleed valve.Every year:Beware that due to the local situation scaling can occur in sample coolerTake note that as indicated in the quotation stage the chlorine level should be max. 300 ppm. Is it higher than you should take into account that corrosion can take place.Change the hydraulic and gearbox oil of the flush pump as described in the manual.We suggest you check the packing of the monoblock and angle valve during stops. If necessary replace them.NCpresentation SPIE27Questions?NCpresentation SPIE28Corriolis Mass Flow measurementDens