The values calculated in this model are best estimates and should be read as calculated design values.
Absorption into spray water in a counter-current packed column · removal efficiency per component, pressure drop and system curve
Each press runs during production hours in cycles: on for the run time, then off for set-up and other stops, so that the on-time share equals the availability. Run and stop times vary randomly by ± the variation, and on Monday every press starts with a random delay of up to the variation × cycle time. After a few cycles the presses run independently, which gives the dynamic total. Statistics are over production time only.
Inlet concentrations follow from the annual solvent load, the production hours, the air flow and the mass %. Hcp at 25 °C in mol/(m³·Pa); B = d ln Hcp/d(1/T) in K; C fraction in g/g; COD factor (ThOD) in g O₂ per g solvent. Spray water: residual after treatment = share of the absorbed solvent that remains in the spray water after water treatment and returns to the top of the column. The model uses it to calculate the concentration in the spray water (mg/l) and includes that in the calculation. Drain water = water leaving the bottom of the column.
Choosing a type or material fills in the fields; you can then adjust them yourself. HTU and pressure drop values are indicative literature values at the reference load (see constants).
HG = HGref·(u/uref)nG·(aw,ref/aw)pG · HL = HLref·(B/Bref)nL·(aw,ref/aw)pL · aw/a according to Onda with constant cO. HTUOG = HG + HL/A. Pressure drop: Δp/H = K·F²·10β·B; flooding at Ffl = Ffl,0·10−γ·B.
1.12. BAT conclusions for flexography and non-publication rotogravure printing (Decision (EU) 2020/2009)
Table 28: BAT-associated emission level (BAT-AEL) for total emissions of VOCs from flexography and non-publication rotogravure printing
Table 30: BAT-associated emission level (BAT-AEL) for VOC emissions in waste gases from flexography and non-publication rotogravure printing
Basis. Commission Implementing Decision (EU) 2020/2009 of 22 June 2020, BAT conclusions for surface treatment using organic solvents (STS), section 1.12 Flexography and non-publication rotogravure printing. Table 28: total VOC emissions from the solvent mass balance < 0.1–0.3 kg VOC per kg solid mass input (yearly average). As an alternative to Table 28, both Table 29 (fugitive VOC emissions < 1–12 % of the solvent input) and Table 30 (TVOC in waste gases 1–20 mg C/Nm³, daily average; upper end 50 mg C/Nm³ if the recovered solvent is reused/recycled) may be used. Total emissions = fugitive emissions + emissions in waste gases (Directive 2010/75/EU, Art. 57(4)). The permit sets the actual value within the BAT-AEL range. Links: BAT conclusions section 1.12 (Tables 28–30) · Decision (EU) 2020/2009, full text · STS BREF (JRC, 2020).
Estimate: the model's efficiency at the average air flow is applied to the whole year; solvent leaving with the waste is not an emission; solvent absorbed in the scrubber water is destroyed in the water treatment (O5) and is therefore not an emission. The solid mass input is an estimate (default 35 % of the solvent input) — replace it with the real figure from the mass balance.
System resistance according to the measured formula Δp = K · Qn (Q in m³/h, Δp in Pa). This is the total air-side pressure drop: packing, demister, ducts and other parts together. Defaults are the values from the BONCUS analysis (K = 2.5·10⁻⁵, n = 1.74). K increases when the column fouls.
The measured K·Qⁿ applies to the packing and spray water flow at the time of measurement (reference below). With the correction on, the difference in wet packing pressure drop between the current settings and the reference is added: Δp = K·Qⁿ + Δppacking(current) − Δppacking(reference).
With automatic selection, shut-off pressure and free-delivery flow are calculated from the maximum flow, the control margin and the ratio Q free / Q max; untick the box to enter them yourself.
The air leaves the column saturated at water temperature (enthalpy method, Merkel). Absorption heat per component from the temperature dependence of the Henry constant: ΔH = B·R. When the equilibrium temperature is below 23 °C, the model calculates with 23 °C and shows the heating needed. Water treatment, tanks and piping outside the column can be included via the extra surface area.
| Symbol / field | Meaning | Unit |
|---|---|---|
| Printing presses (air flow simulation) | ||
| Number of presses | Presses connected to the scrubber; each press has its own settings | – |
| Production days / hours | Production window per week (from Monday 00:00); outside it all presses are off | d, h |
| Base flow | Extraction that is always on during the week (hall ventilation, other sources) | Am³/h |
| Air flow when running | Extraction flow of a press while it is printing | Am³/h |
| Availability | Share of production time that the press is printing; the rest is set-up and other stops | % |
| Average run time per cycle | Average uninterrupted printing period; the stop time follows from the availability: toff = ton·(1 − availability)/availability | h |
| Variation | Random spread of run and stop times (±) and the maximum start delay on Monday (as a share of the cycle time) | % |
| P5 / P95 | Total air flow that is undercut / exceeded during 5 % of the production time; with the link on, P5, the average and the maximum are used as the air flow range | Am³/h |
| Process | ||
| Air flow min / average / max | Air flow at operating conditions (actual m³). The model calculates with the average; minimum and maximum are calculated separately in the "Air flow range" block, with the same solvent load in kg/h | Am³/h |
| Air temperature (dry bulb) | Temperature of the inlet air; together with the humidity needed to convert Am³ to dry Nm³ | °C |
| Anaerobic reactors | Current design: about one anaerobic reactor per 50 m³/h spray water; number = spray water flow / 50 | – |
| COD minimum 650 mg/l | Below this COD in the drain water the concentration is too low for the anaerobic reactors; reduce the spray water flow | mg O₂/l |
| Change of average air flow | Changes the simulated average air flow by this percentage: negative = less air (higher concentration), positive = more air (lower concentration); the solvent load stays the same | % |
| L/G | Liquid-to-gas ratio (calculated): litres of spray water per Am³ of air, QL/QG. The spray water flow is the same at minimum, average and maximum air flow, so L/G changes with the air flow | l/m³ |
| Spray water flow QL | Water distributed over the top of the packing (input, under the chart "Efficiency vs spray water flow"); the chart x-axis scales with it | m³/h |
| Temperature T | Temperature in the column (spray water and air after contact); determines solubility, viscosity and air density. Minimum 23 °C | °C |
| Production hours | Number of hours per year that the line runs and loads the scrubber: production weeks × days per week × hours per day (from the press block) | h/year |
| Solvent input per year | Total solvent input of the installation (I1, incl. solvent in inks). To the scrubber goes the input minus fugitive emission minus solvent in waste | t/year |
| Fugitive emission | Solvent that escapes diffusely (not via the stack) as share of the input; Table 29 of the BAT conclusions | % of input |
| Solvent with waste | Solvent leaving with waste (not an emission) | % of input |
| Solid mass input | Total solids (inks, varnishes, adhesives) used per year; reference for Table 28 | t/year |
| Table 28 limit | Total VOC emissions (stack + fugitive) per kg solid mass input; BAT-AEL < 0.1–0.3, the permit sets the value | kg/kg |
| Table 30 limit | TVOC in the waste gas; BAT-AEL 1–20 mg C/Nm³ (50 with solvent reuse) | mg C/Nm³ |
| Required scrubber efficiency | 1 − (allowed total − fugitive) / solvent to the scrubber | % |
| Wet-bulb temperature | Temperature that water approaches in contact with this air (adiabatic saturation). If the spray water is warmer, the air cools the water by evaporation | °C |
| Max. cooling of spray water | Upper limit per pass if the air leaves the column saturated at water temperature: ṁair·(hsat(Twater) − hin) / (ṁwater·cp). Negative = the air heats the water (condensation) | °C |
| Relative humidity | Humidity of the inlet air at the dry-bulb temperature; used to calculate the dry normal flow | % |
| Normal flow (dry) | QG × 273.15/Tdb × (1 − yH₂O), with yH₂O = RH × psat(Tdb)/101,325 Pa (Magnus), Tdb = dry-bulb temperature | Nm³/h |
| Cin (result) | Total VOC concentration in the inlet air: load (t/year ÷ hours) divided by the dry normal flow (0 °C, 1 atm) | mg/Nm³ |
| Emission after scrubber | Outlet concentration × normal flow × production hours | t/year |
| Column and packing | ||
| D | Internal column diameter | m |
| H (total) | Installed height of the packed bed; used for the pressure drop | m |
| Not effective bottom / top | Part of the bed that does not count for mass transfer (inlet and distribution zone); Heff = H − bottom − top | m |
| Practical efficiency limit | Highest efficiency per component achievable in practice (distribution, channelling, entrainment). If a component comes out higher in theory, an alarm is shown; with the tick box the model calculates with this limit | % |
| Bypass | Share of the air that effectively passes the packing untreated (channelling, poor distribution); limits the maximum efficiency to 100 − bypass | % |
| a | Specific geometric surface area of the packing | m²/m³ |
| HGref | Height of a gas-side transfer unit at the reference conditions (uref, Bref, σc,ref) | m |
| HLref | Height of a liquid-side transfer unit at the reference conditions | m |
| K | Dry packing pressure drop constant: Δpdry/H = K·F² | Pa/m per (Pa½)² = 1/m |
| β | Increase of pressure drop due to water: Δpwet = Δpdry·10β·B | per m³/(m²·h) |
| Ffl,0 | Gas load factor at which the column floods at (almost) zero water | Pa½ |
| σc | Critical surface tension of the packing material; higher = better wetting (PP ≈ 30, PVC ≈ 40, stainless steel ≈ 75) | mN/m |
| Solvent mix | ||
| Mass % | Share of the component in the VOC mass at the inlet; normalised if the sum is not 100 | % |
| Hcp 25 °C | Henry solubility constant at 25 °C (concentration in water / partial pressure); higher = more soluble | mol/(m³·Pa) |
| B | Temperature dependence: Hcp(T) = Hcp,25·exp(B·(1/T − 1/298.15)) | K |
| C fraction | Mass fraction of carbon in the molecule, for conversion to mg C/Nm³ | g C/g |
| COD factor (ThOD) | Theoretical oxygen demand for complete oxidation to CO₂ and H₂O. For these solvents the measured COD (dichromate method) is practically equal to the ThOD | g O₂/g |
| Inlet mg VOC/Nm³ | Inlet concentration of the component: Cin × mass % (calculated) | mg/Nm³ |
| Inlet mg C/Nm³ | The same inlet concentration expressed as carbon: mg VOC/Nm³ × C fraction (calculated) | mg C/Nm³ |
| Spray water: residual after treatment | Share of the solvent absorbed in the column that remains in the spray water after water treatment and returns to the top of the column (0 = completely clean spray water) | % |
| Spray water in | Calculated concentration in the spray water: xin = residual × xout, solved together with the column balance. Sets a lower limit for the outlet (Kaw·xin) and is included in the efficiency | mg/l |
| COD spray water in / drain water out | COD of the water entering the top of the column and leaving the bottom, per component: concentration × COD factor. Total row = sum; total residual % = mass-weighted (Σ in / Σ out) | mg O₂/l |
| Pressure drop and system (all air side) | ||
| K (system) | Resistance factor in Δp = K·Qn for the whole air system (packing, demister, ducts). From the measured data of the BONCUS installation; increases with fouling | Pa/(m³/h)n |
| Packing/water correction | Adds the change in wet packing pressure drop relative to the reference conditions of the measurement (spray water flow, packing height, Kdry, β), so that a higher water flow, a taller bed or a denser packing raise the system pressure drop | Pa |
| n (system) | Exponent in Δp = K·Qn; determines the shape of the system curve (2 = fully turbulent) | – |
| ηfan | Overall fan efficiency, for the shaft power P = Q·Δp/η | – |
| Constants | ||
| cO | Constant in the Onda correlation for the wetted area: aw/a = 1 − exp(−cO·(σc/σ)0.75·Re0.1·Fr−0.05·We0.2) | – |
| nG | Exponent of the gas velocity in HG = HGref·(u/uref)nG·(aw,ref/aw)pG | – |
| nL | Exponent of the liquid load in HL = HLref·(B/Bref)nL·(aw,ref/aw)pL | – |
| pG | Exponent of the wetted area in HG (Onda: 1) | – |
| pL | Exponent of the wetted area in HL (Onda: ⅓) | – |
| uref | Gas velocity at which HGref applies | m/s |
| Bref | Liquid load at which HGref and HLref apply | m³/(m²·h) |
| σc,ref | Material at which HGref and HLref apply (default PP) | mN/m |
| γ | Decrease of the flooding point with liquid load: Ffl = Ffl,0·10−γ·B | per m³/(m²·h) |
| Results | ||
| u | Gas velocity over the empty column cross-section | m/s |
| F | Gas load factor u·√ρG | Pa½ |
| B (liquid load) | Water flow per m² of column cross-section | m³/(m²·h) |
| Wetting rate (MWR) | Liquid load per m² of packing surface, B/a; guide value ≥ 0.08 | m³/(m·h) |
| Wetted area aw/a | Share of the packing surface that is wet (Onda) | % |
| Flooding load | F as a percentage of Ffl; above ≈ 70–80 % the pressure drop rises quickly | % |
| Kaw (m) | Dimensionless Henry coefficient: concentration in air / concentration in water at equilibrium | – |
| A | Absorption factor QL/(m·QG); with A < 1 the water limits the efficiency to about A | – |
| HTUOG | Height of a transfer unit for the component: HG + HL/A | m |
| NTU | Number of transfer units in the bed: Heff/HTUOG | – |
| Efficiency η | 1 − Cout/Cin per component and in total (including bypass) | % |
| Outlet as C | Residual emission converted to carbon, as in the solvent emission limits | mg C/Nm³ |
| Uptake in water | Dissolved solvents in the drained wash water, as concentration, load and COD load | g/l · kg/h · kg COD/h |
| System pressure drop | Total air-side pressure drop at the set air flow: K·QGn. This is the operating point on the system curve | Pa |
| Packing pressure drop (model estimate) | Pressure drop across the wet packed bed only, according to the packing model (Kdry, β); for comparison, already included in the system total | Pa |
| Fan power | Shaft power at the operating point: Q·Δp/η | kW |
| Motor + VFD efficiency | Combined efficiency of electric motor and variable frequency drive; electrical power = shaft power / this efficiency | – |
| Electricity price | Price per kWh for calculating the annual electricity cost of the fan | €/kWh |
| Annual energy use | Electrical power at the average air flow × production hours per year | MWh/year |
| Heat balance on/off | On: the water temperature follows from the steady-state heat balance (min. 23 °C); off: the set water temperature is used | – |
| Outside temperature | Ambient temperature for the wall loss | °C |
| Extra heat input | Heat added to the spray water (heater, heat exchanger with waste heat, pump heat) | kW |
| Shell height | Height of the column shell that loses heat (packing, sump, distributor, demister) | m |
| Extra surface | Additional heat-losing surface of tanks, piping and water treatment at the same U-value | m² |
| U-value wall | Overall heat transfer coefficient from water/air inside to outside air, incl. wind; uninsulated PP ≈ 7, steel ≈ 12, insulated 50 mm ≈ 0.7 | W/(m²·K) |
| Heat from water to air | ṁair·(hsat(Twater) − hin); negative = the air heats the water (condensation) | kW |
| Absorption heat | Σ absorbed mass × ΔHabs, with ΔHabs = B·R/M per component | kW |
| Equilibrium water temperature | Temperature at which heat to the air + wall loss equals absorption heat + extra heat input | °C |
| Heating needed | Extra heat needed to keep the water at the temperature used (23 °C if the equilibrium is lower) | kW |
| Evaporation | Water evaporated into the air, ṁair·(Wsat(Twater) − Win); needs to be made up | kg/h |
| Nominal frequency | Mains frequency at which the fan curve applies (100 % speed) | Hz |
| Frequency at maximum flow | Control margin: with automatic selection the fan is chosen so that the maximum flow is reached at this frequency | Hz |
| Minimum frequency | Lowest frequency at which the motor may run continuously (cooling); below this the flow can only be reduced with a damper | Hz |
| Q free / Q max | With automatic selection: free-delivery flow of the fan divided by the maximum process flow; determines the steepness of the curve | – |
| Shut-off pressure p₀ | Fan pressure at zero flow (damper closed) at nominal frequency | Pa |
| Free-delivery flow | Fan flow without back pressure at nominal frequency | m³/h |
| Fan frequency | Frequency required for a flow: f = fnom·√(Δpsystem(Q)/p₀ + (Q/Qfree)²) | Hz |