U.S. patent application number 14/409781 was filed with the patent office on 2016-02-04 for method and apparatus for treating acidic tail gas by using ammonia process flue gas.
This patent application is currently assigned to JIANGSU NEW CENTURY JIANGNAN ENVIRONMENTAL PROTECTION CO., LTD.. The applicant listed for this patent is JIANGSU NEW CENTURY JIANGNAN ENVIRONMENTAL PROTECTION CO., LTD.. Invention is credited to Guoguang FU, Jing LUO, Changxiang XU, Yanzhong XU.
Application Number | 20160030883 14/409781 |
Document ID | / |
Family ID | 51790990 |
Filed Date | 2016-02-04 |
United States Patent
Application |
20160030883 |
Kind Code |
A1 |
XU; Changxiang ; et
al. |
February 4, 2016 |
METHOD AND APPARATUS FOR TREATING ACIDIC TAIL GAS BY USING AMMONIA
PROCESS FLUE GAS
Abstract
A flue gas-treating method for treating acid tail gas by using
an ammonia process, comprising the following steps of: 1)
controlling the concentration of sulfur dioxide in an acid tail gas
entering an absorber to be .ltoreq.30,000 mg/Nm.sup.3; 2) spraying
and cooling with a process water or/and an ammonium sulfate
solution in the inlet duct of the absorber or inside the absorber;
3) providing an oxidation section in the absorber, wherein the
oxidation section is provided with oxidation distributors for
oxidizing the desulfurization absorption solution; 4) providing an
absorption section in the absorber wherein the absorption section
achieves desulfurization spray absorption by using absorption
solution distributors via an absorption solution containing
ammonia; the absorption solution containing ammonia is supplied by
an ammonia storage tank; 5) providing a water washing layer above
the absorption section in the absorber, wherein the water washing
layer washes the absorption solution in the tail gas to reduce the
slip of the absorption solution; 6) providing a demister above the
water washing layer inside the absorber to control the
concentration of mist droplets contained in the cleaned tail gas.
In the coal chemical industry, the integration of the Claus sulfur
recovery process and the ammonia desulfurization technology can
reduce the investment of the post-treatment and simplify the
operation process, and provide intensive advantages to the
environmental control of plants.
Inventors: |
XU; Changxiang; (Nanjing,
Jiangsu, CN) ; LUO; Jing; (Nanjing, Jiangsu, CN)
; FU; Guoguang; (Nanjing, Jiangsu, CN) ; XU;
Yanzhong; (Nanjing, Jiangsu, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JIANGSU NEW CENTURY JIANGNAN ENVIRONMENTAL PROTECTION CO.,
LTD. |
Nanjing, Jiangsu |
|
CN |
|
|
Assignee: |
JIANGSU NEW CENTURY JIANGNAN
ENVIRONMENTAL PROTECTION CO., LTD.
Nanjing, Jiangsu
CN
|
Family ID: |
51790990 |
Appl. No.: |
14/409781 |
Filed: |
April 24, 2013 |
PCT Filed: |
April 24, 2013 |
PCT NO: |
PCT/CN2013/074657 |
371 Date: |
March 23, 2015 |
Current U.S.
Class: |
423/243.01 ;
422/170 |
Current CPC
Class: |
B01D 53/507 20130101;
B01D 53/79 20130101; B01D 2252/102 20130101 |
International
Class: |
B01D 53/50 20060101
B01D053/50; B01D 53/79 20060101 B01D053/79 |
Claims
1. A flue gas-treating method for treating acid tail gas by using
an ammonia process, characterized in that, comprising the following
steps of: 1) according to the concentration of sulfur dioxide in
the tail gas, adding air into the raw tail gas to make the
concentration of sulfur dioxide reach a suitable absorbing
condition; the concentration of sulfur dioxide to be introduced
into the absorber is .ltoreq.30,000 mg/Nm3; 2) setting process
water spray cooling and/or ammonium sulfate solution spray cooling
in the inlet duct of the absorber or inside the absorber, in order
to cool and wash the tail gas; when using the ammonium sulfate
solution spray cooling, the concentration of ammonium sulfate
solution is increased; 3) providing an oxidation section in the
absorber, wherein the oxidation section is provided with oxidation
distributors for oxidizing the desulfurization absorption solution;
4) providing an absorption section in the absorber wherein the
absorption section achieves sulfurization spray absorption by using
absorption solution distributors via an absorption solution
containing ammonia; the absorption solution containing ammonia is
supplied by an ammonia storage tank; 5) providing a water washing
layer above the absorption section in the absorber, wherein the
water washing layer washes the absorption solution within the tail
gas to reduce the slip of the absorption solution; 6) providing a
demister above the water washing layer inside the absorber to
control the content concentration of mist droplets contained in the
cleaned tail gas; the process of the flue gas-treating method for
treating acid tail gas by using an ammonia process is described as
follows: the concentration of sulfur dioxide in the acid tail gas
is adjusted through adding air from an air blower inside the inlet
duct of the absorber; the process gas flows into the absorber after
being cooled by the cooling spray layer at the inlet of the
absorber or/and by the cooling spray layer of the ammonium sulfate
solution in the absorber; sulfur dioxide is removed after being
cleaned by the absorption spray layer inside the absorber; after
washing and absorption in the water washing layer, the mist
droplets are removal via the demister, and the cleaned tail gas is
discharged from a stack through a cleaned gas duct.
2. The flue gas-treating method for treating acid tail gas by using
an ammonia process according to claim 1, characterized in that, the
absorption solution circulation is an one-stage absorption solution
circulation or a two-stage absorption solution circulation; the
two-stage circulation system is the concentration and
crystallization circulation of the cooling spray solution, wherein
the ammonium sulfate solution is pumped by a cooling washing pump
from an ammonium sulfate storage tank into the cooling washing
spray layer inside the absorber and/or into the cooling washing
layer at inlet of the absorber to cool the flue gas, while the
ammonium sulfate solution evaporates, concentrates, or even
partially crystallized.
3. The flue gas-treating method for treating acid tail gas by using
an ammonia process according to claim 1, characterized in that, the
temperature of the acid tail gas flowing into the absorption spray
layer in the absorber is .ltoreq.80.degree. C.; the operation
temperature of the absorption spray layer in the absorber is
.ltoreq.65.degree. C.; the temperature of absorption solution is
.ltoreq.65.degree. C.
4. The flue gas-treating method for treating acid tail gas by using
an ammonia process according to claim 3, characterized in that, the
superficial gas velocity is 1.5 m/s to 4 m/s; the liquid gas ratio
of the cooling absorption solution is .ltoreq.6 L/m3; the liquid
gas ratio of absorption spraying is 1 L/m3 to 15 L/m3; the
concentration of the ammonium sulfate solution is .gtoreq.15%.
5. The flue gas-treating method for treating acid tail gas by using
an ammonia process according to any one of claims 1-4,
characterized in that, the acid tail gas ammonia desulfurization
treatment is an ammonia desulfurization treating process for
treating the acid tail gas from the Claus sulfur recovery process
or the improved Claus sulfur recovery process, and the cooling
process is achieved by air supplement, water cooling and/or
ammonium sulfate solution cooling.
6. A flue gas-treating apparatus for treating acid tail gas by
using an ammonia process, characterized in that, comprising an
absorber (16), an air blower (2), an ammonia solution tank (3), an
absorber oxidation section (4), an absorption circulation pump (5),
an ammonium sulfate storage tank (6), an ammonium sulfate discharge
pump (7), an inlet duct of the absorber (8), a cleaned gas duct
(9), a stack (10), a demister (11), a water washing layer (12), an
absorber absorption spray layer (13), a cooling washing pump (14),
an inlet cooling washing spray layer (15), and a spraying pump
(17), wherein the inlet duct is connected to the air blower (2); a
process water or/and ammonium sulfate solution cooling and spraying
device is set in the inlet duct of the absorber or inside the
absorber; an oxidation section (4) is provided in the absorber
(16), wherein the oxidation section (4) is provided with oxidation
distributors for oxidizing the desulfurization absorption solution;
an absorption section is provided in the absorber (16) wherein the
absorption section achieves desulfurization spray absorption by
using absorption solution distributors via an absorption solution
containing ammonia; an oxidation blower (1) is provided in the
oxidation section (4); a solution generated by the oxidation
section (4) is transported into the ammonium sulfate storage tank
(6) and transported out of the apparatus by an ammonium sulfate
discharge pump (7); the cooling spray layer is the cooling spray
with a coverage rate over 200%, while the absorption spray layer
(13) consists of two to four layers of spray with the spray tower
type or the packed tower type, and the spray coverage rate for each
layer is more than 250%.
7. The flue gas-treating apparatus for treating acid tail gas by
using an ammonia process according to claim 6, characterized in
that, the water washing layer (12) with a packed tower type is
provided above the absorption spray layer (13), the demister is set
at the top of the absorber, and the cleaned gas duct and stack are
provided above the absorber.
8. The flue gas-treating apparatus for treating acid tail gas by
using an ammonia process according to claim 6, characterized in
that, a centrifugal air blower is used to adjust the concentration
of acid tail gas by supplying air, and the pressure and flow amount
thereof are set according to the parameters of the acid tail gas to
ensure the concentration of sulfur dioxide in the tail gas to be no
more than 30,000 mg/Nm3.
9. The flue gas-treating apparatus for treating acid tail gas by
using an ammonia process according to claim 6, characterized in
that, an oxidation air blower is used to oxidize ammonium sulfite
to ammonium sulfate and supply the oxidation air, wherein the
pressure of the air blower is set according to the liquid level of
the oxidation section and is no less than 0.05 MPa, and the flow
rate of the oxidation air is more than 150% of a theoretical
value.
10. The flue gas-treating apparatus for treating acid tail gas by
using an ammonia process according to claim 6 or 7, characterized
in that, the height of the absorber is 20 m to 40 m; the oxidation
residence time in the oxidation section (4) is over 30 minutes, and
gas-liquid distributors with a plate type or a grid type are
provided, and the superficial gas velocity at the absorption spray
layer (13), the water washing layer (12), and the demister is 1 m/s
to 5 m/s, and the demister (11) has 2 to 3 baffle plates.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a purification technology and an
apparatus for industrial flue gas such as an acid tail gas (flue
gas) or the like in chemical (coal chemical) process. Specifically,
the invention relates to a desulfurization technology and an
apparatus using ammonia as the absorbent to remove sulfur dioxide
from a flue gas and yield a fertilizer as a byproduct. This
invention belongs to the technical fields of environmental
protection, power and chemical industry or the like.
BACKGROUND OF THE INVENTION
[0002] Sulfur dioxide discharged from industrial processes is the
major source of acid rain and sulfur dioxide pollution. In order to
control sulfur dioxide emission to improve environmental quality,
industrial flue gas desulfurization is necessary and must be
enforced.
[0003] Acid tail gas generally refers to the tail gas generated
from the following steps: a sulfur-containing gas generated from
the chemical (especially coal chemical) process firstly goes
through the recovery process to recover sulfur, phenols,
naphthalenes and so on, and then is sent to the incinerator to
fully combust the organic compounds and hydrogen sulfide. The main
hazardous component in the acid tail gas is high-concentration
sulfur dioxide, which needs to be treated in the desulfurization
unit in order to meet the emission regulations.
[0004] In the coal chemical industry, the Claus sulfur recovery
process is usually used for removing hydrogen sulfide and
recovering sulfur. In order to ensure that the tail gas meet the
emission standards, the SuperClaus, EuroClaus or SCOT technology is
usually used to treat the tail gas from the conventional two-stage
Claus sulfur recovery unit. All these processes have the
disadvantages of complicated process, high investment, high
operating cost, difficult operation or the like. For example,
CN200710049014 improves the low-temperature Claus sulfur recovery
process by mixing an acid gas and air for Claus reactions to take
place inside the combustion chamber, and using the process gas from
the first stage of the waste heat boiler as the reheating source.
This invention contains a gas-gas heat exchanger, which utilizes
the process gas at the first stage of waste heat boiler, or the
flue gas at the outlet duct of the incinerator at 600.degree. C. as
the reheating resource for the subsequent reactors. The second
stage to the fourth stage reactors and the third stage to the fifth
stage sulfur condensers are controlled by a switching valve
program. In each switching cycle, two of the three reactors undergo
low-temperature absorption while the other reactor undergoes
temperature ramp up, stable regeneration, gradual cooling, and
stable cooling. Such control is complicated, and if stable control
cannot be achieved, the sulfur recovery efficiency will be greatly
affected.
[0005] Sodium carbonate and sodium hydroxide are used previously
for the removal of sulfur dioxide from acid tail gas in small-scale
chemical processes. This method also has the disadvantages of high
capital and operating costs, and complicated operation or the like.
Coal chemical industry which uses atmospheric fixed-bed gasifier
with lump coal as raw material often uses atmospheric pressure
desulfurization technology by installing an absorber operated at
atmospheric pressure (20 kPa) in the coal gasification process. At
present in China, the circulation and regeneration of kauri
solution is often used for desulfurization, and then the sulfur
recovery devices are used to generate sulfur.
[0006] At present, limestone desulfurization is widely used for
treating flue gas from coal-fired boilers. Capital and operating
costs for limestone desulfurization device are high, and
especially, it requires high-quality limestone, and the market for
the desulfurization byproduct (gypsum) is limited. Waste water
generated from this process has to be disposed. Sodium carbonate
and sodium hydroxide desulfurization, which is often used in acid
tail gas desulfurization treatment, consumes sodium carbonate and
sodium hydroxide, and the market for its byproduct sodium sulfate
is limited, resulting in high operating cost and poor
reliability.
[0007] With the wide applications of ammonia desulfurization
technology, the advantages of this method become more and more
significant. Benefiting from its advantages such as high
efficiency, no secondary pollution, byproduct recycle, simple
process, and integrability with boiler flue gas desulfurization,
the ammonia desulfurization technology can be applied to more
industrial processes. For example, in coal chemical industry,
two-stage Claus sulfur recovery can be combined with ammonia
desulfurization, achieving over 99.5% desulfurization
efficiency\and 95% sulfur recovery. The byproduct ammonium sulfate
can be sold directly, there is no secondary pollution, the process
is simple and easy to operate, and the capital and operating costs
are low. The integrated design combining the byproduct generated
from ammonia desulfurization treatment with that from the boiler
ammonia desulfurization can further reduce the investment of the
post-treatment system and simplify the process flow. This method
simplifies the environmental protection emission control in these
plants and benefits the plant operation management.
SUMMARY OF THE INVENTION
[0008] The purpose of this invention is to provide a method for
treating acid tail gas by using an ammonia process and an apparatus
thereof. Especially the combination of the Claus process and the
ammonia desulfurization technology can effectively improve the acid
tail gas desulfurization efficiency, and effectively control the
ammonia slip and the aerosol generation. In addition, this process
is simple and operating cost is low. The desulfurization efficiency
is .gtoreq.95%, and the ammonia recovery ratio is
.gtoreq.96.5%.
Technical Solution of the Invention
[0009] The application provides a flue gas-treating method for
treating acid tail gas by using an ammonia process and an apparatus
thereof, including the following:
[0010] 1) according to the concentration of sulfur dioxide in the
flue gas (tail gas), supplying air to make the concentration of
sulfur dioxide reach a suitable absorbing condition; and the acid
tail gas ammonia desulfurization treatment is carried out inside
the absorber; the concentration of sulfur dioxide to be introduced
into the absorber is .ltoreq.30,000 mg/Nm.sup.3;
[0011] 2) setting process water spray cooling and/or ammonium
sulfate solution spray cooling in the inlet duct of the absorber or
inside the absorber to cool and wash the tail gas, so as to make
the flue gas meet the absorbing condition of desulfurization. The
concentration of ammonium sulfate increases when the ammonium
sulfate solution is used for the spray cooling. Such increase makes
the ammonium sulfate solution concentrate or even crystallize, and
generates products with different concentrations.
[0012] 3) providing an oxidation section in the absorber, wherein
the oxidation section is provided with oxidation distributors for
oxidizing the desulfurization absorption solution in order to
ensure the oxidation efficiency of the absorption solution to be
over 98%.
[0013] 4) providing an absorption section in the absorber wherein
the absorption section achieves desulfurization spray absorption by
using absorption solution distributors via an absorption solution
containing ammonia. This setting ensures the desulfurization
efficiency to be over 95%.
[0014] 5) providing a water washing layer above the absorption
section in the absorber, wherein the water washing layer washes the
absorption solution droplets in the tail gas to reduce the slip of
the absorption solution as well as to control the water washing
flow in order to keep the concentration of the absorption
solution.
[0015] 6) providing a demister above the water washing layer inside
the absorber to control the mist droplets concentration in the
cleaned tail gas.
Process Flow of the Invention is as Follows
[0016] The process of the flue gas-treating method for treating
acid tail gas by using an ammonia process and the apparatus is
described as follows: the sulfur dioxide concentration of the flue
gas is adjusted through supplying air from the air blower 2 at the
inlet of the absorber 8. Then the flue gas flows into the absorber
16 after being cooled through the washing cooling spray layer 15 at
inlet of the absorber 16 or after being cooled by the cooling spray
layer 17 using ammonium sulfate solution inside the absorber.
Sulfur dioxide is then removed by washing within the absorption
spray layer 13 inside the absorber 16. After the absorption through
water washing layer 12 and the removal of mist droplets through the
demister 11, the cleaned gas is discharged from the stack 10
through the cleaned gas duct 9.
[0017] Cooling of the flue gas can be achieved by supplementing air
and spraying process water or/and ammonium sulfate solution.
[0018] Furthermore, the circulation of the absorption solution can
be a one-stage circulation or a two-stage circulation. If ammonium
sulfate solution with low concentration is required to be generated
from the absorber, one-stage absorption solution circulation system
is adequate. If ammonium sulfate solution with high concentration
or ammonium sulfate crystal slurry is required to be generated from
the absorber, two-stage absorption solution circulation system
shall be used. The functions of the first-stage absorption solution
circulation system are absorption and oxidation. The circulation
pump 5 draws the absorption solution out from bottom of the
absorber to the absorption spray layer 13 inside the absorber for
spraying. The absorption solution contacts the process gas inside
the absorber to wash and absorb sulfur dioxide, and generate
ammonium sulfite. Absorption solution containing ammonium sulfite
contacts the oxidation air supplied by the oxidation air blower 1
to the oxidation section 4 at the bottom of the absorber 16 to
generate ammonium sulfate after oxidation. Ammonia is supplied from
the ammonia solution storage tank 3. The second-stage absorption
solution circulation system is a cooling spray (concentration and
crystallization) circulation, in which the process gas is cooled by
ammonium sulfate solution pumped from the ammonium sulfate solution
storage tank 6 into the cooling washing spray layer 17 inside the
absorber and/or into cooling washing layer 15 at the inlet of the
absorber, and the ammonium sulfate solution evaporates,
concentrates or even crystallizes. Solution/slurry generated from
the absorber is transported by the ammonium sulfate discharge pump
7, and is used to produce solid ammonium sulfate or the like, or
directly used.
Main Parameters in the Invention
[0019] Optimal concentration of sulfur dioxide in the process gas
entering the absorber is no more than 30,000 mg/Nm.sup.3;
[0020] Optimal temperature of process gas entering the absorption
spray layer of absorber is no more than 80.degree. C.;
[0021] Operating temperature of the absorption spray layer inside
the absorber is no more than 65.degree. C.;
[0022] The temperature of the absorption solution is no more than
65.degree. C.;
[0023] The superficial gas velocity is 1.5 m/s to 4 m/s;
[0024] The liquid-gas ratio of the cooling and washing liquid is no
more than 6 L/m.sup.3;
[0025] The liquid-gas ratio of the spraying absorption solution is
1 L/m.sup.3 to 15 L/m.sup.3;
[0026] The concentration of the ammonium sulfate solution is no
less than 15%.
[0027] This invention can be the acid tail gas ammonia
desulfurization treatment process following the Claus sulfur
recovery process (including refined Claus process and boiler flue
gas ammonia desulfurization unit).
[0028] The invention provides a flue gas-treatment apparatus for
treating acid tail gas by using an ammonia process, comprising an
absorber 16, an air blower 2, an ammonia solution storage tank 3,
an absorber (a desulfurization tower) oxidation section 4, an
absorber recirculation pump 5, an ammonium sulfate storage tank 6,
an ammonium sulfate discharge pump 7, an inlet duct of the absorber
8, a cleaned gas duct 9, a stack 10, a demister 11, a water washing
layer 12, an absorption spray layer 13 inside the absorber 16, a
cooling washing pump 14, an inlet cooling washing spray layer 15
and a spraying pump 17. The inlet duct of the absorber is connected
to the air blower 2 and there are cooling and spraying devices 15
and 17 set in the inlet duct of the absorber 16 or inside the
absorber with the process water or/and the ammonium sulfate
solution. There is an oxidation section 4 set inside the absorber
16, and oxidation distributors are set inside the oxidation section
4 to achieve the oxidation of the desulfurization absorption
solution. There is an absorption section 13 set inside the absorber
16, and the absorption section 13 uses absorption distributors to
achieve the desulfurization spraying absorption via absorption
solution containing ammonia. The oxidation section 4 is equipped
with an oxidation blower 1, and the solution generated from the
oxidation section 4 is transported into the ammonium sulfate
storage tank 6 and transported out of the device by the ammonium
sulfate discharge pump 7.
[0029] The cooling spray layer 17 is the one with the spraying
coverage rate over 200%, while the absorption spray layer 13 uses
two to four layers of spray of the spray tower type or the packed
tower type, and the spray coverage rate for each layer is more than
250%. The water washing layer 12 of the packed tower type is set
above the absorption spray layer 13. The demister 11 is set on the
top part of the absorber 16. The cleaned gas duct 9 and stack 10
are directly connected to the absorber 16 from its top.
[0030] An air blower 2 of centrifugal type is used to adjust the
concentration of acid tail gas, and the pressure and flow rate can
be adjusted according to the parameters of the acid tail gas, in
order to ensure the concentration of sulfur dioxide in the tail gas
to be no more than 30,000 mg/Nm.sup.3.
[0031] The oxidation air blower 1 is the device to supply oxidation
air to oxidize ammonium sulfite into ammonium sulfate. The pressure
of the blower is set according to the liquid level of oxidation
section and shall be no less than 0.05 MPa. In addition, the flow
rate of the oxidation air shall be larger than the 150% of the
theoretical value.
[0032] The height of the absorber 16 is 20 m to 40 m. The oxidation
residence time in the oxidation section 4 is no less than 30
minutes, and gas-liquid distributors of plate/grid-type are set in
the oxidation section 4. The superficial gas velocity of the
absorber at the absorption spray layer 13, the water washing layer
12, and the demister 11 is 1 m/s to 5 m/s. The demister 11 uses 2-3
baffle plates.
Benefits of the Invention
[0033] This invention provides a process scheme of desulfurizing
acid tail gas with high efficiency, low investment and full
utilization. The integrated design combining the byproduct
generated from acid gas ammonia desulfurization unit with the
boiler ammonia desulfurization units can reduce investment of the
post-treatment system and simplifies the process flow. This method
intensifies the environmental control for plants, and benefits the
operation management.
[0034] Spray cooling with process water and/or the ammonium sulfate
solution is set in the inlet duct of the absorber or inside the
absorber to cool the acid tail gas entering the absorber to below
125.degree. C., and also to save energy consumed in the evaporation
crystallization of ammonium sulfate. In addition, supplying air to
achieve a proper acid tail gas concentration broadens the
industrial applications of ammonia desulfurization process. For
example, in coal chemical industry, if the Claus sulfur recovery
process is combined with the ammonia desulfurization technology,
over 99.5% desulfurization efficiency and about 95% sulfur recovery
efficiency can be achieved. The byproduct ammonium sulfate can be
sold directly, there is no secondary pollution, the process is
simple and easy to operate, and the capital and operating costs are
low. The technology does not require complicated control in the
Claus sulfur recovery process or other refined Claus processes.
Sulfur that cannot be recovered in the Claus process can be
recovered by the method described in this invention, which
effectively improves the desulfurization efficiency and controls
ammonia slip and aerosol generation. In addition, this process is
simple and the operating cost is low. This invention, with
excellent performance in terms of desulfurization efficiency and
ammonia recovery, provides a novel solution for air pollution
control problems such as the haze which happened frequently in
China recently. The byproducts of the ammonia desulfurization can
be used effectively, making this process more economically viable.
The design of the devices in this invention is also simple and
reliable. The combination of a cooling spray layer and an
absorption spray layer a, as well as a blower with adjustable flow
rate make it more convenient to treat acid tail gas in time.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 shows an apparatus and flow chart of this
invention;
[0036] FIG. 2 shows an ammonia desulfurization apparatus and flow
chart for treating acid tail gas from a natural gas plant;
[0037] FIG. 3 shows an ammonia desulfurization apparatus and flow
chart for treating acid tail gas from the Claus sulfur recovery
process in a coal chemical plant;
[0038] FIG. 4 shows an ammonia desulfurization apparatus and flow
chart for treating chemical acid tail gas;
[0039] FIG. 5 shows an ammonia desulfurization apparatus and flow
chart for treating acid tail gas with Claus sulfur recovery of an
oil refinery;
[0040] An oxidation air blower 1, an air blower 2, an ammonium
solution storage tank 3, an absorber (desulfurization tower)
oxidation section 4, an absorption recirculation pump 5, an
ammonium sulfate storage tank 6, an ammonium sulfate discharge pump
7, an inlet duct of the absorber 8, a cleaned gas duct 9, a stack
10, a demister 11, a water washing layer 12, an absorber absorption
spray layer 13, a cooling washing pump 14, an inlet cooling washing
spray layer 15, an absorber 16, a spraying pump (ammonia solution
pump) 17, an acid tail gas inlet 18, air 19, ammonia 20, process
water 21, finished ammonium sulfate or semi-finished ammonium
sulfate 22.
DETAILED DESCRIPTION OF THE INVENTION
[0041] The process of this invention can be divided into the
following five steps:
[0042] A. Adjustment of the Concentration of Sulfur Dioxide in Acid
Tail Gas
[0043] The sulfur dioxide concentration in the acid tail gas
entering the absorber is adjusted according to product
specifications, water balance and oxidation velocity, etc., and the
concentration is usually no more than 30,000 mg/Nm.sup.3, which can
be achieved by supplying air to the acid tail gas through the air
blower.
[0044] B. Cooling of the Acid Tail Gas, and Absorption Solution
Concentration (Crystallization)
[0045] The temperature of the acid tail gas is usually over
120.degree. C., which shall be cooled down to no more than
80.degree. C. before the sulfur dioxide absorption. The method is
using process water and ammonium sulfate solution to wash the tail
gas, and a washing layer can be set in the inlet duct of the
absorber or inside the absorber. When ammonium sulfate solution is
used to reduce the temperature of the acid tail gas, water in the
ammonium sulfate solution evaporates to increase the concentration
and crystals can even be generated in the solution. Concentration
of the product is determined according to the balance and
requirements of the process water.
[0046] C. Sulfur Dioxide Absorption
[0047] Process gas with the temperature between 40.degree. C. and
80.degree. C. or less goes through the absorption reaction after
reacting with the absorption solution at the absorption cooling
layer of the absorber, and then sulfur dioxide is removed, and
ammonium sulfite is generated. The method is circulating the
absorption solution by an absorption circulating pump, and then
feeding the absorption solution into the oxidation section in the
absorber for oxidation.
[0048] D. Ammonium Sulfite Oxidation
[0049] The oxidation section is set under the absorption spray
layer or at the bottom of the absorber. Ammonium sulfite generated
from the absorption of sulfur dioxide enters the oxidation section
to be oxidized into ammonium sulfate by oxidation air (including
air, oxygen-enriched air or pure oxygen). The method is setting
oxidation distributors at the oxidation section inside the
absorber, and oxidation air is supplied by an oxidation blower. If
the concentration of the absorption solution is low, methods such
as jet flow or the like can also be used for the oxidation.
[0050] E. Washing and Demisting of the Process Gas
[0051] Process gas with sulfur dioxide removed contains absorption
solution droplets, which shall be washed off by water at the spray
layer. Water droplets within the process gas after washing will be
removed by the demister above to reduce the water consumption and
the impact to the environment.
Characteristics of the Main Devices Related to this Invention
[0052] 1) Absorber
[0053] Absorber, the core device used in this process, is usually
cylindrical, but can also be square or other shapes. From bottom to
top, the absorber can be divided into an oxidation section, a
cooling and washing layer (a concentration and crystallization
section), an absorption spray layer, a water washing layer, and a
demister. The superficial gas velocity is 1.5 m/s to 4 m/s.
[0054] A) Oxidation Section
[0055] Oxidation section can be set at the bottom of the absorber
or outside of the absorber, and its diameter and height are
determined according to the oxidation demand. Normally, the
oxidation residence time is no less than 0.5 h.
[0056] Liquid-gas distributors are set inside the oxidation
section, so as to ensure good contact between liquid and gas.
Devices such as jet flow or the like can also be used for
oxidation.
[0057] B) Cooling Spray Layer
[0058] Cooling spray layer uses water or/and ammonium sulfate
solution to cool the acid tail gas. Normally, a water spraying
device or/and an ammonium sulfate spraying device are set. The
water spraying device is set inside the inlet process gas duct,
while the ammonium sulfate spraying device is set on the aforesaid
duct or inside the absorber according to the requirement. Coverage
rate of the cooling spray layer is more than 200%, the total
spraying flow rate is no less than 4 times of water evaporation
rate, and the liquid-gas ratio is no less than 6 L/m.sup.3.
[0059] C) Absorption Spray Layer
[0060] Absorption spray layer is set at the middle-upper part of
the absorber normally of spray tower type, or of the combination of
spray tower type and packed tower type. According to the
concentration of sulfur dioxide in the acid tail gas, two to four
layers of spray are placed, while the spraying coverage rate of
each layer is over 250%.
[0061] D) Water Washing Layer
[0062] Water washing layer of packed tower type is set above the
absorption spray layer. The water flow rate is determined according
to water balance.
[0063] E) Demister
[0064] Demister is set at the top part of the absorber, and
demister which can be placed horizontally can also be set in the
cleaned gas duct of the absorber. Demister of baffle plate type is
usually selected, and regular packing can also be used as demister
if there is no ash deposition. The superficial gas velocity of the
demister is 3 to 4.5 m/s.
[0065] 2) Air Blower
[0066] Air blower is used to adjust the concentration of sulfur
dioxide in the acid tail gas, and centrifugal blower is often used.
The air pressure and the flow rate are set depending on the
parameters of acid tail gas to ensure the sulfur dioxide
concentration of the acid tail gas to be no more than 30,000
mg/Nm3.
[0067] 3) Oxidation Air Blower
[0068] Oxidation air blower is the device to supply oxidation air
for oxidizing ammonium sulfite into ammonium sulfate. The pressure
of the blower is set according to liquid level of oxidation
section, and it is usually no less than 0.05 MPa. In addition, the
flow rate shall be 150% of the theoretical value or more.
EXAMPLE 1
FIG. 2 Shows an Ammonia Desulfurization Apparatus for Treating Acid
Tail Gas From a Natural Gas Plant
[0069] The total flow rate of acid tail gas is 13,375 Nm.sup.3/h,
the temperature is 152.degree. C., the concentration of sulfur
dioxide in the acid tail gas is 31,443 mg/Nm.sup.3, and the
pressure is 100,000 Pa. The absorbent is aqueous ammonia with a
concentration of 15%.
[0070] Process flow and devices: FIG. 2 shows the process flow
diagram and devices. After the acid tail gas is supplemented with
ambient-temperature air by the air blower 2, the concentration of
sulfur dioxide is decreased to 22,000 mg/Nm.sup.3 and the
temperature is decreased to 115.degree. C. The temperature of acid
tail gas is further decreased to 70.degree. C. at inlet of the
absorber by being cooled with process water and ammonium sulfate
solution spray layer 15 (process water flow rate is 0.2 m.sup.3/h
and ammonium sulfate solution flow rate is 20 m.sup.3/h). Then the
flue gas enters the absorber 16 to be sprayed with absorption
solution. Then the process gas is cleaned by three absorption
solution spray layers 13, and absorption solution flow rate is 40
m.sup.3/h in each layer. The sulfur dioxide concentration is
decreased to 60 mg/Nm.sup.3 (86 mg/Nm.sup.3 under the conditions of
the original acid tail gas with 99.7% desulfurization efficiency).
Process gas at 47.degree. C. is then cleaned by water washing layer
12, demisted by demister 11, and then discharged from stack 10.
[0071] The absorption solution with sulfur dioxide absorbed is
oxidized to ammonium sulfate solution by oxidation air from the
oxidation air blower 1 in the oxidation section 4 at the bottom of
the absorber. Ammonium sulfate solution flows into the ammonium
sulfate storage tank 6, and transported by the ammonium sulfate
discharge pump into ammonium sulfate system of the boiler flue gas
ammonia desulfurization plant Ammonia from the ammonia solution
storage tank 3 is pumped into the bottom of the absorber by the
ammonia solution pump 17 to adjust the pH of the absorption
solution.
Main Features of Devices
[0072] The absorber 16 is made of 316L stainless steel with the
total height of 29 m. Diameter of the oxidation section 4 is 4 m
and the gas-liquid distributors is of grid type. The absorption
spray layer 13, with a diameter of 2 m, has three layers of
spraying distributors and each layer has 3 spray nozzles. Diameter
of water washing layer 12 is 2 m with 200 mm of corrugated
packaging.
[0073] Diameter of the demister 11 is 2 m with two baffle plates
and the material is enhanced PP. The type of the air blower 2 is
centrifugal blower made of carbon steel with rated flow of 7,000
Nm.sup.3/h and rated output pressure of 2,500 Pa. Two air blowers
are required, with one for redundancy. The ammonia solution storage
tank 3 is made of carbon steel and the volume is 50 m.sup.3.
[0074] Te ammonia solution pump 17 is made of stainless steel with
the rated flow of 4 m.sup.3/h. The oxidation air blower 1 is a
piston-type air compressor with rated flow of 15 m.sup.3/min and
rated output pressure of 2.0 MPa. Two air blowers are required with
one for redundancy.
[0075] The absorption circulation pump is made of 316L stainless
steel with rated flow of 40 m.sup.3/h. Three absorption circulation
pumps are required, and each absorption recycle pump covers to one
layer of absorption spraying distributors.
[0076] Operation parameters and results: 15% ammonia solution is
consumed at 1,531 kg/h, and 25% ammonium sulfate solution is
produced at 3,460 kg/h, and the ammonia recovery efficiency is
97%.
[0077] The sulfur dioxide concentration in the cleaned gas is 60
mg/Nm.sup.3 (the concentration is 86 mg/Nm.sup.3 under the
condition of acid tail gas and the desulfurization efficiency is
99.7%).
[0078] The process flow diagram of the ammonia desulfurization for
treating acid tail gas from a natural gas plant shown in FIG. 2
also includes acid tail gas 23 and ammonia solution 24 from the
natural gas plant.
EXAMPLE 2
The Ammonia Desulfurization Apparatus for Treating Tail Gas From
the Claus Sulfur Recovery Process From a Coal Chemical Plant
[0079] Acid tail gas from the Claus sulfur recovery unit of a coal
chemical plant is generated from acid gas after going through a
two-stage Claus sulfur recovery process, a tail gas incinerator and
a waste heat boiler. The total flow rate of acid tail gas is 59,912
Nm.sup.3/h, the temperature is 165.degree. C., the concentration of
sulfur dioxide in the acid tail gas is 12,600 mg/Nm.sup.3, and the
oxygen concentration is 2% and the pressure is 0.02 MPa. The
absorbent is 99.6% anhydrous ammonia.
Process Flow
[0080] FIG. 3 shows the process flow chart. The acid tail gas flows
into the absorber 16 after being cleaned and cooled to around
100.degree. C. by process water (1 m.sup.3/h) spray layer 15 at the
inlet of the absorber, and then the gas is cleaned by the washing
and cooling spray layer 2 (ammonium sulfate solution, 120
m.sup.3/h) inside the absorber. After the process gas is cooled to
about 70.degree. C., the process gas enters the upper part of the
absorber 16, and is cleaned by three absorption spray layers 13,
and absorption solution flow rate at each layer is 140 m.sup.3/h.
The sulfur dioxide concentration is decreased to 80 mg/Nm.sup.3
with the desulfurization efficiency of 99.4%. Process gas with the
temperature of 47.degree. C. is cleaned by the water cleaning layer
12, and eliminated droplets by the demister 11 and then discharged
from the stack 10.
[0081] After absorbing sulfur dioxide, the absorption solution is
oxidized into ammonium sulfate solution by the oxidation air from
the oxidation air blower 1 at the oxidation section 4 at the bottom
of the absorber. Ammonium sulfate solution enters ammonium sulfate
storage tank 6, and is then pumped by the cooling washing pump 14
to the washing and cooling spray layer 2 inside the absorber to
clean the process gas. After the washing and cooling processes,
ammonium sulfate flows back to the ammonium sulfate storage tank
6.
[0082] The concentration of ammonium sulfate in the absorption
solution at the oxidation section is controlled around 20%, while
that in the ammonium sulfate tank is around 45%. The output is
transported into the ammonium sulfate evaporation and
crystallization device in the plant by the ammonium sulfate
discharge pump for the production of solid ammonium sulfate.
[0083] Anhydrous ammonia from the anhydrous ammonia storage tank 3
is pumped into the absorber by the liquid ammonia pump 17 (or by
its own pressure if the temperature is high enough) to adjust the
pH of the absorption solution.
Main Features of Devices
[0084] The absorber 16 is made of carbon steel with a glass flake
lining for anti-corrosion. It is 32 m in height and the diameter is
4 m.
[0085] Gas-liquid distributors are set inside the oxidation section
4. A washing and cooling spray layer 2 is set inside the absorber
with four spray nozzles at each layer. An absorption spray layer 13
with three layers of spraying distributors are set at the upper
part of the washing and cooling spray layer 2, and each layer has 5
spray nozzles. Absorption spray layer 13 is separated from the
washing and cooling spray layer 2 by air cap.
[0086] A 200 mm of corrugated packing is set in the water washing
layer 12.
[0087] Demister 11 uses two layers of baffle plates with the
material of enhanced PP.
[0088] The ammonia solution storage tank 3 is made of carbon steel
with the volume of 50 m.sup.3.
[0089] The ammonia solution pump is made of stainless steel with
the rated flow of 4 m.sup.3/h.
[0090] Air blower 1 is a screw air compressor with the rated flow
of 40 m.sup.3/min, and the rated output pressure is 2.0 MPa. Two
air blowers are required, as one is working while the other one is
standing by.
[0091] The absorption circulation pump is made of 2605 stainless
steel with the rated flow of 140 m.sup.3/h. Three absorption
circulation pumps are required, and each absorption recycle pump
covers to one layer of absorption spraying distributors.
[0092] The cooling washing pump is made of 2605 stainless steel
with the rated flow of 120 m.sup.3/h. Two pumps are required, as
one is working while the other one is standing by.
Operation Parameters and Result
[0093] 99.6% anhydrous ammonia is consumed at 412 kg/h, 45%
ammonium sulfate solution is produced at 3,438 kg/h, and the
ammonia recovery efficiency is 97.1%. The concentration of sulfur
dioxide in the cleaned gas is 80 mg/Nm.sup.3 with the
desulfurization efficiency of 99.4%.
[0094] The process flow diagram of the ammonia desulfurization
process for treating the acid tail gas from the Claus sulfur
recovery process of a coal chemical plant shown FIG. 3 also
includes coal chemical Claus sulfur recovery acid tail gas 25 and
liquid ammonia 24.
EXAMPLE 3
Ammonia Desulfurization Devices for Treating Acid Tail Gas From a
Chemical Project
[0095] Acid gas with sulfur and organic waste liquid generated from
a chemical project is burned inside a incinerator, and the heat is
recycled by a waste heat boiler to produce the byproduct steam, and
then generates acid tail gas with sulfur dioxide. The total acid
tail gas flow rate is 11,018 Nm.sup.3/h, the temperature is
350.degree. C., the concentration of sulfur dioxide is 2.57% (v%),
that the concentration of oxygen is 6.22%, and the the pressure is
5,000 Pa.
[0096] The absorbent is 99.6% anhydrous ammonia.
Process Flow
[0097] FIG. 4 shows the process flow chart. The concentration of
sulfur dioxide in acid tail gas is reduced to 6680 mg/Nm.sup.3
after the supplement of ambient-temperature air from the air blower
10, and then the temperature is decreased to 60.degree. C. The acid
tail gas is cleaned and cooled by spraying process water (0.5
m.sup.3/h) in the spray layer 15 at inlet of the absorber, and then
the process gas goes into the absorber 16, and is cleaned by the
washing and cooling spray layer 2 (the flow of ammonium sulfate
solution is 140 m.sup.3/h) inside the absorber. After the process
gas is cooled to around 50.degree. C., the process gas enters the
upper part of the absorber 16, and is cleaned by three absorption
spray layers 13, and the spray rate of the absorption solution at
each layer is 160 m.sup.3/h. The concentration of sulfur dioxide is
then reduced to 30 mg/Nm.sup.3 (the concentration is 321
mg/Nm.sup.3 under the acid tail gas condition with desulfurization
efficiency of 99.6%). Process gas at 48.degree. C. is cleaned by
the water cleaning layer 12 and demisted by the demister 11 before
being discharged from the stack 10.
[0098] The absorption solution which has absorbed sulfur dioxide is
oxidized to ammonium sulfate solution by oxidation air from the
oxidation air blower 1 in the oxidation section 4 at the bottom of
the absorber. Ammonium sulfate solution enters the ammonium sulfate
storage tank 6, and then is pumped by the cooling washing pump 14
to the washing and cooling spray layer 2 inside the absorber to
clean process gas. After the washing and cleaning processes,
ammonium sulfate flows back to the ammonium sulfate storage tank
6.
[0099] The ammonium sulfate concentration in the absorption
solution at the oxidation section is controlled at around 30%,
while the concentration of solid ammonium sulfate in the absorption
solution of ammonium sulfate tank is around 10%. The output is
transported by the ammonium sulfate discharge pump to the plant for
solid-liquid separation in post-treatment system. The mother liquor
generated from the solid-liquid separation in post-treatment system
is sent back to the ammonium sulfate storage tank 6 for circulation
crystallization.
[0100] Anhydrous ammonia from the ammonia storage tank 3 is pumped
into the absorber by the liquid-ammonia pump 17 (or by its own
pressure if the temperature is high enough) to adjust pH of the
absorption solution.
Main Features of the Devices
[0101] The absorber 16 is made of carbon steel with glass flake
lining for anti-corrosion. It is 31 m in height and the diameter is
4.8 m. Gas-liquid distributors are set inside the oxidation section
4.
[0102] A washing and cooling spay layer 2 is set inside the
absorber with nine spray nozzles at each layer. An absorption spray
layer 13 with three-layer spraying distributors is equipped at the
upper part of washing and cooling spray layer 2, and each layer has
11 spray nozzles. The absorption spray layer 13 is separated from
the washing and cooling spray layer 2 by air cap. The water washing
layer 12 has a ripple packing in 200 mm. Demister 11 uses two
layers of baffle plates with enhanced PP.
[0103] The ammonia solution storage tank 3 is made of carbon steel
with the volume of 120 m.sup.3. Two tanks are required with one for
redundancy.
[0104] The material of ammonia solution pump 17 is stainless steel
with the rated flow of 1 m.sup.3/h. The air blower 1 is a roots
compressor with the flow rate of 50 m.sup.3/min, and the rated
output pressure of 0.15 MPa. Two pieces are needed with one for
redundancy. The material of absorption circulation pump is 2605
stainless steel with the rated flow of 160 m.sup.3/h. Three pieces
are needed with one absorption circulation pump corresponding to
one layer of absorption spraying distributors. The material of
cooling washing pump is 2605 stainless steel with the rated flow of
140 m.sup.3/h. Two pieces are required, as one is working while the
other one is standing by.
Operation Parameters and Result
[0105] 99.6% anhydrous ammonia is consumed at 431 kg/h, solid
ammonium sulfate is produced at 1618 kg/h, and the ammonia recovery
efficiency is 97.1%.
[0106] The concentration of sulfur dioxide in the cleaned gas is 30
mg/Nm.sup.3, while that of sulfur dioxide under the condition of
acid tail gas is 321 mg/Nm.sup.3, and the desulfurization
efficiency is 99.6%.
[0107] The process flow diagram of ammonia desulfurization for
treating chemical acid tail gas shown in FIG. 4 also includes
mother liquor 31 in the ammonium sulfate post-process system, and
the cleaned gas discharge 27.
EXAMPLE 4
An Ammonia Desulfurization Apparatus for Treating Acid Tail Gas
From the Claus Sulfur Recovery Process From an Oil Refinery
[0108] Acid tail gas from the Claus sulfur recovery unit of an oil
refinery is generated from acid gas after going through a two-stage
Claus sulfur recovery process, a tail gas incinerator, and a waste
heat boiler. The total acid tail gas flow rate is 61,221
Nm.sup.3/h, the temperature is 160.degree. C., the concentration of
sulfur dioxide in acid tail gas is 10,200 mg/Nm.sup.3, the oxygen
concentration is 7%, and the pressure is 0.02 MPa. The absorbent is
99.6% anhydrous ammonia.
Process Flow
[0109] Please refer to FIG. 5 for ammonia desulfurization flow
chart for the tail gas with the Claus sulfur recovery process from
an oil refinery. The acid tail gas is cleaned and cooled by the
process water (at 1 m.sup.3/h) spray layer 15 at the inlet of the
absorber with temperature lowering to around 100.degree. C., and
then flows into the absorber 16. After that, the process gas is
cleaned by washing and cooling spray layer 2 (ammonium sulfate
solution is at 120 m.sup.3/h) inside the absorber. After the
temperature of process gas is reduced to around 70.degree. C., the
process gas flows into the upper part of the absorber 16, and is
cleaned by three absorption spray layers 13, and the flow rate of
the absorption solution at each layer is 140 m.sup.3/h. The
concentration of sulfur dioxide is reduced to 80 mg/Nm.sup.3 with
the desulfurization efficiency of 99.2%. The process gas with the
temperature of 46.degree. C. is cleaned by the water cleaning layer
12, and eliminated mist droplets by the demister 11 before being
discharged out of the stack 10.
[0110] The absorption solution with sulfur dioxide absorbed is
oxidized to ammonium sulfate solution by oxidation air from the
oxidation air blower 1 in the oxidation section 4 at the bottom of
the absorber. Ammonium sulfate solution enters the ammonium sulfate
storage tank 6, and then is pumped by the cooling washing pump 14
to the washing and cooling spray layer 2 inside the absorber to
clean the process gas. After the washing and cooling processes,
ammonium sulfate flows back to the ammonium sulfate storage tank
6.
[0111] The concentration of ammonium sulfate in the absorption
solution at the oxidation section is controlled at around 20%,
while that in the ammonium sulfate tank is around 45%. The 45%
ammonium sulfate solution is transported to the ammonium sulfate
evaporation and crystallization unit by the ammonium sulfate
discharge pump for solid ammonium sulfate production.
[0112] Anhydrous ammonia from the ammonia storage tank 3 is pumped
into the absorber by the ammonia pump 17 (or by its own pressure if
the temperature is high enough) to adjust the pH of the absorption
solution.
Main Features of Devices
[0113] The absorber 16 is made of carbon steel with glass flake
lining for anti-corrosion. The absorber is 24 m in height and the
diameter is 4 m.
[0114] A washing and cooling spay layer 2 is set inside the
absorber with four spray nozzles at each layer. An absorption spray
layer 13 with three layers of spraying distributors is set at the
upper part of the washing and cooling spray layer 2, and each layer
has 5 spray nozzles. The absorption spray layer 13 is separated
from the washing and cooling spray layer 2 by air cap.
[0115] A 200 mm corrugate packing is set in the water washing layer
12.
[0116] Demister 11 uses in two baffle plates with the material of
enhanced PP.
[0117] The ammonia solution storage tank 3 is made of carbon steel
with the volume of 50 m.sup.3.
[0118] The ammonia solution pump 17 is made of stainless steel with
the rated flow of 4 m.sup.3/h.
[0119] The air blower 1 is a screw air compressor with the rated
flow of 40 m.sup.3/min, and the rated output pressure is 2.0 MPa.
Two air blowers are required, as one is working while the other one
is standing by.
[0120] The absorption circulation pump is made of 2605 stainless
steel with the rated flow of 140 m.sup.3/h. Three absorption
circulation pumps are required, and each absorption recycle pump
covers to one layer of absorption spraying distributors.
[0121] The cooling washing pump is made of 2605 stainless steel
with the rated flow of 120 m.sup.3/h. Two pumps are required, as
one is working while the other one is standing by.
[0122] The oxidation tank is made of carbon steel with glass flake
lining for anti-corrosion. It is 4.5 m in height and the diameter
is 10 m. Gas-liquid distributors are set in the oxidation tank
4.
Operation Parameters and Result
[0123] 99.2% anhydrous ammonia is consumed at 341 kg/h, 45%
(weight) ammonium sulfate solution is produced at 2,840 kg/h, and
the ammonia recovery efficiency is 97.3%.
[0124] The sulfur dioxide concentration of the cleaned gas is 80
mg/Nm.sup.3 with removal efficiency of 99.2%. Acid tail gas 30 from
the sulfur recovery incinerator is also included in FIG. 5.
* * * * *