NON-CONDENSIBLE GAS SYSTEM

The collection and disposal of foul and malodorous gases in a Noncondensible Gas
System provide an effective means of mill odor control and is mandatory in order to meet
stringent air quality requirements. A. H. Lundberg, Inc. has been actively involved in the
design and installation of these systems in mills for many years. Lundberg
Noncondensible Gas Systems (NCG) have been installed to collect gases from several
emission sources and provide for their disposal by incineration or chemical modification.

Gases containing Total Reduced Sulfur (TRS) compounds are characteristically separated
into two groups. The first group is low concentration-high volume (LCHV) gases. The
second group is high concentration-low volume (HCLV) gases. Typical TRS
concentrations in gases from these emissions are shown in Table I and Table II.


TABLE I: TYPICAL TRS CONCENTRATIONS*
High Concentration - Low Volume

High Concentration    Concentration (PPM by Volume)
Low Volume
Gas Sources    H2S    CH3SH    (CH3)2S     (CH3)2S2

Digester, Batch Blow    0 -    0 -    100 -     10 -
Gases    1,000    10,000    45,000     10,000

Digester, Batch    0 -    10 -    100 -     100 -
Relief Gases    2,000    5,000    60,000     60,000

Digester, Continuous    10 - 300    5,0 0 0 - 1,500 -     5 0 0 -
        10,000 7,500    3,000

Evaporator Hotwell    600 -    300 -    500 -     500 -
    9,000    3,000    5,000     6,000

* U. S. Environmental Protection Agency: Environmental Pollution Control, Pulp and Paper
Industry Part I:    Air



TABLE II: TYPICAL TRS CONCENTRATIONS*
Low Concentration - High Volume
Low Concentration -    Concentration     (PPM by Volume)
High Volume
Gas Sources    H2S    CH3SH (CH3)2S (CH3)2S2

Washer Hood Vent    0 - 5    0 - 5    0 - 15     0 - 3

Washer Seal Tank    0 - 2    10 - 15    10 - 700    1 - 150

Black Liquor    0 - 10    0 - 25    10 - 500     2 - 95
Oxididation Tower
Exhaust

Smelt Dissolving Tank    0-75    0-2    0-4     0-3

Lime Kiln Exhaust    0-250    0-100    0-50      0-20

Lime Slaker Vent    0-20    0-1    0-1      0-1
*Enviromental Protection Agency: Environmental Pollution Control, Pulp and Paper Industry
Part I: Air

A piping system is used to convey the noncondensible gases from the various emission
sources to the point of disposal in the lime kiln, power boiler, or specially designed
incinerator. In systems containing low concentration-high volume gases, an abundance
of dilution air is introduced to keep the NCG mixture below the explosive limit. In a high
concentration-low volume gas collection system, care is taken to exclude air and prevent
dilution into an explosive composition. Before and after air dilution, the explosive limits
of compounds commonly present in NCG streams must also be considered. These limits
are given in Table Ill.
   
TABLE Ill:    LOWER AND UPPER EXPLOSIVE LIMITS OF SOME
COMPONENTS OF KRAFT NON-CONDENSIBLE GASES**
        Lower Explosive    Upper Explosive
Compound Limit, Volume    Limit, Volume
        Percent Percent
Hydrogen Sulfide    4.0    44.0
Methyl Mercaptan    3.9    21.8
Dimethyl Sulfide    2.2    19.7
Dimethyl Disulfide    1.1    16.1
Methanol    6.7    36.0
Turpentine    0.8    *

* Has not been established.
** Beckwith, W.F., "Estimation of Explosive Limits of Noncondensible Gas Mixtures", TAPPI
57 (12):147 (1974).

Turpentine vents, due to the volatile nature of turpentine, are collected separately. This
turpentine-rich source is passed through a direct contact after condenser. The after
condenser is a packed tower containing small diameter rings. The packed tower, even
if operated dry, will act as a small channel type flame arrester. By wet operation, the
lower section of the unit performs as a direct contact condenser and flame arrester. The
upper section of the unit, also packed, serves as a mist eliminator and as a flame
arrester.

Anther consideration in the system design is the flame propagation speed of NCG
mixtures. Lundberg systems are engineered to ensure that the vapor speed is above the
flame propagation speed at all times.

A. H. Lundberg, Inc. NCG Systems are liberally provided with flame arresters and
pressure safety valves or rupture discs for the mechanical protection of equipment and
the safety of operators. Lundberg has designed and now supplies these flame arresters
to meet these specifications.

A typical NCG System equipment arrangement consists of a pair of shut-off valves located at
each emission source which can be isolated. These valves are interlocked, so
that at the decision of the operator, the source is either vented or sent to process. To
back-up these valves in case of valve failure, a safety valve or rupture disc is installed
normally set for about 10 psig. A flame arrester is also installed at each source.

Most noncondensible gas sources are from hot vessels and consequently the gases are
hot and saturated with moisture. Adequate condensing of moisture is essential for
efficient gas combustion. To reduce combustion problems, the gases should be cooled
to the 120 degree F. range. This can be accomplished in an indirect cooler or a direct contact
cooler with indirect heat removal.

Frequently the mill will elect to install a Lundberg high efficiency RSH scrubber ahead of
the gas cooler. In this unit, the collected NCG are passed through a packed column for
removal of hydrgen sulfide and methyl mercaptan by absorption in white liquor. The total
TRS in the NCG stream is reduced by 70% to 80%. Condensate from the cooler can be
added to the white liquor.

Following the gas cooler, the gases are piped to the combustion chamber of the
incinerator, where they are burned at a temperature exceeding 2,000 degrees F. In most
cases the lime kiln is used for incineration. A. H. Lundberg, Inc. also supplies a
dedicated Waste Gas Incinerator.

For satisfactory operation of an NCG system, it frequently requires that the blow heat
system be carefully fine tuned to be sure that surges in the gas flow rate do not occur.
In mills using batch digesters, a gas accumulator (vaporsphere) is sometimes used in the
NCG system. The need for a gas accumulator arises when, during a blow, a surge of
gases occurs as steam displaces air in the blow tank and the top of the hot water
accumulator tank. The gas accumulator employs a flexible diaphragm to control the
momentary surges in gas volume during the initial part of a digester blow and provides
a uniform flow to the incinerator. A. H. Lundberg, Inc. offers gas accumulators of various
designs. We have found, however, that blow heat systems can be designed that do not
require a gas accumulator.

Non-Condensible Gas System Block Diagram

Non-Condensible Gas Sys Collection Point

Non-Cond. Gas Sys. Pipeline Installation

Non-Condensible Gas System Eductor

Noncondensible Gas Collection Inquiry

Date:_________________
Reference: ________________


NONCONDENSIBLE GAS COLLECTION INQUIRY

Sources:

Batch Digesters

Digester Volume________________ ft.3
Digester Numbers__________________
Cooks________________ no./day

Cooking Schedule
    Fill_________________ min.
    To Temp__________________
    At Temp__________________
    Blow_________________

Digester Relief_______________ min.
    Flow ___________________ cfm or lb. steam/min.
No. Simultaneous ___________________
No. Turpentine Condensers___________________ If more than 1
_____ Series
_____ Parallel

Blow Tank
Number___________________
Volume_________________ ft.3
Simultaneous Blows___________________ number

Blow Heat Recovery (Batch)
Padding Steam Used _______ yes ______ no
Gas Accumulator_________________ ft.3 Type ___________

Continuous Digester
Number___________________
Tonnage___________________tons/day
Relief Flow__________________ cfm or lb. steam/min.
Pre-Steamer    __________________ cfm or lb. steam/min.
Flash Tank__________________ cfm or lb. steam/min.

Evaporators
No. Hot Wells________________
Capacity Inlet_________________ lb. evaporator/hr.
Ejector Capacity________________

Weak Black Liquor Storage Tank
Volume_______________________ ft.3
Fill Rate (Max)_______________________gpm
Vent Size_______________________ inch diameter

Strong Black Liquor Storage Tank
Volume____________________ ft.3
Fill Rate (Max)____________________ gpm
Vent Size______________________ inch diameter

Black Liquor Measuring Tank
Volume____________________ ft.3
Fill Rate (Max)____________________ gpm
Vent Size_______________________ inch diameter

Black Liquor Measuring Tank
Volume____________________ ft.3
Fill Rate (Max)___________________ gpm
Vent Size_______________________ inch diameter

Turpentine Decanter Vent
Vent Size    ______________________ inch diameter

Steam Stripper
Type_________TRS__________ TRS + MeOH
NCG Flow_____________________ ft.3/min
NCB Temp.____________________degrees F.

Foul Condensate Storage Tank
Volume_____________________ ft.3
Fill Rate (Max)_____________________gpm
Vent Size______________________ inch diameter

Dissolving Tank Vent
No. Tanks    _____________________
Stack Diameter_______________________ inches
Flow    ______________________ cfm/stack

Brown Stock Washer Hoods
No. Lines_______________________
No. Washers/line______________________
Vent Fan Capacity ______________________ total cfm

Other Sources
________________________________________________________________________________
________________________________________________________________________________


Incineration Desired
    Lime Kilns    _____ yes _____ no
No. of Kilns    _________________
    Power Boilers    _____ yes _____ no
    No. of Boilers    ____________________
    Dedicated Incinerator _____ yes _____ no

RSH Scrubber Required
    White Liquor Temp._______________degrees F.