Size industrial isothermal falling film hydrogen chloride (HCl) gas absorbers with impervious graphite shell-and-tube bundles. Compute exothermic heat of solution, shell-side cooling water demand, graphite tube area, muriatic acid yield, and tube wetting rates.
HCl Feed & Acid Specification
Absorber Sizing & Thermal Duty Outputs
Live Impervious Graphite Falling Film Absorber Cross-Section
Cutaway illustration showing top liquid distributor head, vertical graphite tube bundle, shell-side cooling water jacket, and concentrated acid drain pot.
Fatal Traps & Engineering Pitfalls in Falling Film HCl Absorbers
1. Tube Dry-out from Operating Below Minimum Wetting Rate
If liquid flow drops below Gamma_min (0.12 kg/m·s perimeter), the liquid film tears into rivulets. Dry patches form inside graphite tubes, stopping absorption heat transfer. Dry HCl gas breaks through into the tail-gas system while localized overheating bakes resin impregnant, degrading tube thermal conductivity.
2. Brittle Thermal Shock Fracture of Impervious Graphite Tubes
Impregnated graphite has zero ductile yield. Introducing cold cooling water while the absorber is hot or restarting after an emergency shutdown without ramping water and gas rates synchronously produces steep radial thermal stresses, snapping tubes near tubesheet cement joints and flooding the cooling water loop with acid.
3. Fuming Acid Over-Concentration Past the Solubility Limit
Attempting to produce >36 wt% HCl at cooling water temperatures above 30°C pushes equilibrium vapor pressure beyond atmospheric limits. Dense white fuming fog of aerosolized hydrochloric acid forms inside the tubes, overwhelming vent scrubbers and discharging toxic acid clouds into plant atmosphere.
4. Shell-Side Cooling Water Scaling and Thermal Choking
Operating with cooling water discharge temperature exceeding 45°C causes hard calcium carbonate (CaCO3) scale to precipitate on the external graphite tube surfaces. Because graphite tubes cannot be mechanically drilled without cracking, scale insulates the bundle, collapsing overall U from 750 down to <250 W/m²·K within weeks.
5. Liquid Distribution Cup Plugging and Maldistribution
The top tubesheet relies on precision serrated weir inserts or tangential swirl cups in every tube to establish uniform film thickness. Particulate debris or pipe rust from makeup water lines lodges in these narrow orifices, starving individual tubes of water and triggering local thermal runaway and acid vapor venting.
Thermodynamic Derivations & Sizing Equations
Isothermal falling film absorption couples the intense enthalpy of solution with film hydrodynamic wetting criteria.
M_acid = M_HCl / (w_HCl / 100) [kg/h]
M_water_feed = M_acid - M_HCl [kg/h]
2. Absorption Heat of Solution Duty (Q_abs):
ΔH_abs ≈ 2,080 kJ / kg HCl absorbed
Q_abs = (M_HCl · ΔH_abs) / 3600 [kW thermal duty]
3. Shell-Side Cooling Water Demand:
m_cw = Q_abs / (4.186 · ΔT_cw) [kg/s]
V_cw = m_cw · 3.6 [m³/h]
4. Impervious Graphite Heat Transfer Surface Area:
LMTD = [ (T_acid_out - T_cw_in) - (T_acid_in - T_cw_out) ] / ln[ (T_acid_out - T_cw_in) / (T_acid_in - T_cw_out) ]
A_graphite = (Q_abs · 1000) / (U · LMTD) [m²]
5. Tube Count and Specific Wetting Rate (Γ):
N_tubes = A_graphite / (π · d_i · L_tube)
Γ = M_acid / [ N_tubes · π · d_i · 3600 ] [kg/(m·s) perimeter]