Recovery - Recovery Boiler V1 Model

The Recovery Boiler is used for the combustion of concentrated black liquor and the recovery of inorganic compounds. The recovered inorganic compounds are ultimately recycled for pulping. The black liquor combustion produces energy which is used for steam generation. The model does not include electrostatic precipitators, smelt dissolving tank, air heaters, black liquor preheaters, salt cake mixing tank or steam producing equipment.
The strong black liquor is the liquor at firing conditions at the guns. Air is atmospheric or enriched air at the temperature and pressure at which it is introduced in the furnace. Smelt is the total smelt produced by the furnace. The flue gas is the wet flue gas after the economizer and includes all of the inorganic dust.

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Data Descriptions

Data Unit Description
Set Item Type Native
Equipment Properties RedEff Fraction or Percent Fraction The ratio of Na2S to Na2S plus Na2SO4 in the smelt.
Ash Fraction or Percent Fraction Fraction of nozzle solids in the flue gas.
Fume Fraction or Percent Fraction Weight fraction carbonate in the ash recycles.
FlueO2 Fraction or Percent Fraction Wet basis O2 in the flue gas (volume %).
LHV Enthalpy BTU/lb Higher heating value of the nozzle liquor.
SmeltTemp Temperature F The temperature of the smelt.
FlueTemp Temperature F The temperature of the exiting flue gas.
SteamTemperature Temperature F Steam Temperature. Required if Boiler Feedwater and Steam streams are connected.
SteamPressure Pressure psia Steam Pressure. Required if Boiler Feedwater and Steam streams are connected.
Blowdown Fraction or Percent Fraction Fraction of inlet feed water as blow down.
FlueCO     The CO in the flue gas, ppm wet basis.
FlueSO2     The SO2 in the flue gas, ppm wet basis.
FlueH2S     The H2S in the flue gas, ppm wet basis.
ClEnrich     The Cl enrichment ratio.
KEnrich     The K enrichment ratio.
Carbon Fraction or Percent Fraction The fraction of inlet organics unreacted.
C Fraction or Percent Fraction Mass fraction of C in the nozzle liquor.
H Fraction or Percent Fraction Mass fraction of H in the nozzle liquor. The mass fraction of O is set by difference (1-C-H).
Calculated Properties Available Energy Energy Flow BTU/hr Energy available for steam.
BL Sensible Heat Enthalpy BTU/lb Sensible Heat of heavy black liquor.
Air Sensible Heat Enthalpy BTU/lb Sensible Heat of moist air to the furnace.
Total Heat Input Enthalpy BTU/lb Total heat input.
Dry Gas Heat Loss Fraction or Percent Fraction Dry flue gas sensible heat loss.
Air Moisture Heat Loss Fraction or Percent Fraction Sensible heat loss of moisture in the air.
Comb H2O Heat Loss Fraction or Percent Fraction Latent and sensible heat loss of combustion H2O.
Liquid H2O Heat Loss Fraction or Percent Fraction Latent and sensible heat loss of input liquid H2O.
Molten Smelt Heat Loss Fraction or Percent Fraction Molten smelt heat loss.
Na2S Heat Loss Fraction or Percent Fraction Heat loss for producing Na2S.
Misc Heat Loss Fraction or Percent Fraction Radiation and unaccounted heat loss.
Total Heat Loss Fraction or Percent Fraction Total heat loss.
Thermal Efficiency Fraction or Percent Fraction Thermal efficiency.
Steam DeltaH Enthalpy BTU/lb Enthalpy rise in steam. Enthalpy of steam minus enthalpy of boiler feed water.
Steam to Solids Ratio     Steam to solids ratio. Steam flow out divided by black liquor solids in.
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Equipment Properties

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Example of using equipment

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Method&Equations

The method used by the Recovery Boiler is based on the TAPPI Short-Form calculation. Black liquor is composed of H2O, dissolved inorganics and dissolved organics. The dissolved inorganics are carried as ions (i.e., Na+, OH-, HS-, SO4--, CO3--, etc.). The composition of dissolved organics is unknown. However, from analysis of mill black liquor a total ultimate analysis of the liquor can be obtained. The mass fraction of carbon and the mass fraction of hydrogen from this analysis are normally used as the inputs to the model. By summing total inorganic components (Na+, S--, K+, Cl-) and adding the mass of carbon and hydrogen from the ultimate analysis, it is assumed that the remaining mass is oxygen. This composition is used by the model and is assumed to correspond to the specified higher heating value.
If ash recycle is specified the following rules are applied to the ash:
    Total ash recycle quantity = Frac Ash Recycle * total nozzle black liquor solids
    Ash recycle fraction Cl = Cl enrichment ratio * fraction Cl in the nozzle black liquor solids
    Ash recycle fraction K = 2.25 * fraction K in the nozzle black liquor solids
    Ash recycle fraction CO3 = Frac Fume Carbonate
    All ash recycle K forms K2SO4, Cl forms NaCl and CO3 forms Na2CO3
    The remaining ash is Na2SO4
After calculating the K2SO4, NaCl, Na2CO3 and Na2SO4 in the ash the remaining Na, K, S, Cl and CO3 is in the smelt. All Cl in the smelt forms NaCl. The amount of air (excess air) required is determined iteratively. The remaining sulfur forms Na2S, K2S, Na2SO4 and K2SO4. The sulfur used by Na and K is based on the Na to K ratio. The formation of sulfates is based on the specified reduction efficiency. Any remaining Na forms Na2CO3 and any remaining K forms K2CO3. The remaining C forms CO2. Once all the compounds containing oxygen are determined the theoretical amount of O2 required is set and the air stream flow can be calculated.

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Warnings

Zero flow entering!

Steam pressure greater than feed water pressure!

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Errors

Missing a stream. Check connections!

Negative elemental O2 in BL!

Req sulfur > avail sulfur!

No air needed. Check Recovery Boiler data!

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