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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 |
Unit |
Description |
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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 |
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The CO in the flue gas, ppm wet basis. |
| FlueSO2 |
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The SO2 in the flue gas, ppm wet basis. |
| FlueH2S |
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The H2S in the flue gas, ppm wet basis. |
| ClEnrich |
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The Cl enrichment ratio. |
| KEnrich |
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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 |
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Steam to solids ratio. Steam flow out divided by black liquor solids in. |
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.
Zero flow entering!
Solution: Set nonzero inlet air and liquor flows.
Steam pressure greater than feed water pressure!
Solution: Set water inlet pressure higher than steam pressure.
Missing a stream. Check connections!
Solution: Check if all the streams are connected to the equipment.
Negative elemental O2 in BL!
Solution: Set lower ultimate analysis C and H fractions.
Req sulfur > avail sulfur!
Solution: Set lower reduction efficiency.
No air needed. Check Recovery Boiler data!
Solution: Check the settings.
Warnings 