C+A
THERMORIGENERATIVE
COMBUSTOR FOR
CHLORINATED OFF-GAS
A SPECIFIC DESIGN FOR THE
CHEMICAL-PHARMACEUTICAL
INDUSTRY
WHY AN AD HOC COMBUSTOR
FOR CHLORINATED OFF-GAS?
1.
The resort to organo-chlorinated solvents in
the synthesis of pharmaceutical intermediate
products, sometimes only during well defined
campaigns, comes from the high
characteristics of these compounds, which are
often unreplaceable.
2.
Under combustion chlorinated compounds
produce HCl (hydrochloric acid). In some
cases HCl is present in the off-gas input as
well.
WHY AN AD HOC COMBUSTOR
FOR CHLORINATED OFF-GAS?
3.
The thermorigenerative combustor type is the highest
efficiency combustor: it has the lowest support fuel
consumption and exit temperatures of 60 ÷ 150°C. It is
of simple construction but materials generally adopted
result to be unfit for chlorinated off-gas.
4.
In the combustor flue gases HCl has a dew point of ab.
200°C. Below this temperature HCl condensation (very
corrosive) finds place. For T < 100°C condensation of
water vapour produced by combustion brings in dilution
of HCl condense, so decreasing the overall
corrosiveness, which nonetheless remains high.
REFERENCE DESIGN
PARAMETERS
Data apply to off-gas
thermorigenerative
combustors in the
Lombardia Region Italy (D.g.r. 1.08.2003
n. 7/12943 – Utilzation
of best available
technologies PC.T.02).
The following main
parameters apply:
Organic Combustion Combustion
chlorine in chamber
chamber
the VOC temperature residence
[% p.]
[°C]
time
[sec]
Absent
≥ 750
≥ 0,6
≤ 0,5
≥ 850
≥ 1,0
> 0,5 e ≤
2,0
> 2,0
≥ 950
≥ 2,0
≥ 1100
≥ 2,0
POSSIBLE TECHNICAL SOLUTIONS
After a careful study and examination of what has been
been done in this field in Italy and Europe up till now,
the technical solutions appear to be:
SOLUTION A (high energy consumption)
Enhancing the chlorinated off-gas inlet temperature
to T ≥ 200°C by a heat exchanger - 270°C overheated
steam / off-gas or double heat exchanger - 200°C
steam/ off-gas and NG flue gases / off-gas), with
relating high costs of heat exchangers (graphite) and of
utilities.
POSSIBLE TECHNICAL SOLUTIONS
SOLUTION B (with minimized energy consumption)
Feeding the off-gas (chlorinated and non) directly to
combustor, with no preheat, under the same conditions
of off-gas release from production, or after scrubbers
that may be introduced to reduce high concentration
peaks of chlorinated compounds (alkaline scrubbing).
Feeding auxiliary fuel (natural gas) for combustion
chamber temperature control, leaving the combustor
flue gas temperature uncontrolled: this shall then
depend upon off-gas input flow (turn-down) and organic
concentration / enthalpy of combustion.
BASE POINTS OF C+A PROJECT
SOLUTION A
Plant capacity
10.000 Nm3/h
SOLUTION B
(C+A)
Plant capacity
10.000 Nm3/h
Steam consumption (15 bar
g - 200°C) for off-gas
preheat
686 Kg/h
0 Kg/h
Natural gas consumption
(34,953 KJ/Nm3) for offgas preheat
32 Nm3/h
0 Nm3/h
131,000 Euro/year
0 Euro/year
Yearly cost (5,000 hrs/year)
of steam and natural gas
for off-gas preheat
COMPARISON OF UTILITIES CONSUMPTION AND RELATING COSTS
FOR SOLUTIONS A AND B – 10,000 NM3/H OFF-GAS PLANT
BASE POINTS OF C+A PROJECT
Natural gas
Diluted off-gas
Concentr. off-gas
Hot gas by-pass
3 tower combustor
Steam ejector
Flue gas duct
NaOH 30%
Scrubber-quencher
Salty drain
Flue gas fan
Final chimney
OVERALL OFF-GAS INPUT FLOW: 5,000 ÷ 70,000 NM3/H
BASE POINTS OF C+A PROJECT
Plant guaranteed emission concentrations:
COMBUSTOR
[mg/Nm3]
TOC
CO
NOx
HCl
< 20
< 100
< 100
SCRUBBER
[mg/Nm3]
< 10
Values refer to measured oxygen level (= O2 as such)