The Shell Denox & Dioxin Destruction System

The Shell DeNOx & Dioxin Destruction System

CRI Catalyst Company (

CRI Asia Pacific, Business manager, Dr. Harry Tang

65-276-3631

1.The present state of the technology

The catalytic system use Shell’s proprietary catalyst and reactor technology, specifically developed for industrial plants to meet the new stringent NOx and dioxin emission standards. The catalyst’s high reactivity is well suited for low temperature retrofit application. In addition, the Shell systems require much less plot-space for equipment and lower pressure-drop.

Typical applications include municipal and waste incineration plants, gas turbines, co-generation units, gas-fired heaters and boilers, ethylene cracking furnaces, as well as nitric acid and caprolactum plants.

2.The outline and principles of the technology

Shell developed its proprietary Lateral Flow Reactor (LFR) and low-temperature DeNOx catalyst technology in the 1980’s. Later, Shell introduced the dioxin destruction catalyst technology in the early 1990’s. As environmental awareness grows and air quality standards become more stringent around the world, the Shell DeNOx System (SDS) and the Shell Dioxin Destruction System (SDDS) have emerged as the best available control technologies for low-temperature applications in Europe, USA and Asia.

CRI, a member of the Royal Dutch/Shell group of companies, has built up a wide experience of treating flue gases from both small (2,000 Nm3/h) and large (>1,000,000 Nm3/h) processes. Typical components removed from the flue gas include NOx, CO, N2O, NH3, VOC’s and dioxins.

2.1The Shell DeNOx System (SDS)

The Shell DeNOx System belongs to the Selective Catalytic Reduction (‘SCR’) category of NOx removal technology. This process converts NOx in flue-gases with ammonia over a catalyst to environmentally inert compounds, water and nitrogen.

The SDS is superior to other, conventional SCR systems based on so-called honeycombs, in two important respects; a) the catalyst and b) the modular reactor system.

a)The catalyst is a commercially manufactured extrudate consisting of a proprietary mix of titanium/vanadium components. This form allows a ready diffusion of NOx molecules to the high internal surface area, resulting in a very high intrinsic activity. Consequently, it is possible to achieve very high NOx removal efficiencies, even at relatively low operating temperatures, typically 160 – 380°C.

b)The reactor system is based on LFR modules, as shown in Fig. 1, filled with catalyst. This design ensures that 100% of the flue gas passes through the catalyst. As the gas passes through a thin layer of catalyst very low pressure drops are possible.

Fig. 1. Lateral Flow Reactor (LFR) module with catalyst

The SDScombination of a highly active catalyst and LFR modules gives significant design flexibility. It is possible to optimize designs for each combination of plant conditions, NOx conversion, NH3 slip, temperature, pressure drop and available plot space.

2.2The Shell Dioxin Destruction System (SDDS)

The Shell Dioxin Destruction System is a proven low temperature technology for dioxin emission reduction. Unlike technologies based on carbon adsorption where the dioxins are only transferred to solid particles, which require further processing, The SDDSdestroys the dioxin compounds in a single process step. The SDDS uses a Shell proprietary catalyst to convert dioxins to a mixture of harmless gases. A typical reaction is shown below.

C12HNCI8-NO2+(9+0.5n)O2 (n-4)H2O+12CO2+(8-n)HCI

The process does not require the addition of any reactant. Only oxygen in the flue gas is required for the destruction.

The combination of the high activity catalyst with the LFR (Fig. 1) allows the SDDS to easily achieve high dioxin conversions. From inlet concentrations of up to 100ngTEQ/Nm3, the Shell Dioxin Destruction System can achieve over 99.9% destruction of dioxins and furans, down to emission limits of less than 0.1–0.01ngTEQ/Nm3.

3.The processes and contents of the technology developed or improved

The basic exploratory work has been carried out in conjunction with the group of Processor Rappe at the University of Umea in Sweden. Processor Rappe is recognized as a world expert in the field of dioxins. This work has concentrated on confirming that dioxin destruction occurs rather than just adsorption. The work has made use of 14C labeled dioxins to track the reaction pathway.

3.1The Umea reactor

The 5 kW lab-scale incinerator unit (Fig. 2) isequipped with a fluidized bed through which primary airis fed. There are also two radial inlets of secondary airabove the sand bed. The fuel is fed onto the bed aspellets (6 mm outer diameter) via a motorized screw. Thefuel used was an artificial municipal solid waste (MSW)designed to reflect the contents of real waste, primarilyin Sweden (Wikstrom and Marklund, 1998). The temperatureof the bed and freeboard was around 800°C.The convector part (boiler) consists of five 3 m long steeltubes with temperatures from 600°C down to 200°C inthe last section. After this a cyclone is placed, followedby a coarse metal filter for particle removal, and a lime filter to reduce SO2 and HCl flue gas concentrations tolevels more typical of post-air pollution control conditions.A summary of operating conditions is shown inTable 1. Themain gas stream went through a wet scrubber and finallythrough a carbon chemical filter (activated carbon,KMnO4, Al2O3), before entering the atmosphere by wayof a fan.The combustion gases CO2 and O2 were continuouslymeasured with IR and zirkonium sensors while SO2,HCl and particle contents were determined off-line.

Fig. 2. Schematic view of the Umea laboratory scale fluidized bed reactor and the location of the SDDS

Table 1. Typical Umea lab-scale incinerator operation conditions during the experiment with the SDDS

Combustion efficiency
Bed and freeboard temperature
O2-level / 99.5%
780±30°C
10.5±3.5% / Particle contenta
HCl concentrationa
SO2a / ~170 mg/Nm3
~240 mg/Nm3
~30 mg/Nm3

aSampled after coupling point to SDDS as seen in Fig. 2

3.2The SDDS reactor

After the lime filter (Fig. 2, coupling point) a side stream was led first through an additional less coarse metal filter, then via heated tubing to the heated catalytic reactor (Fig. 3, SDDS). This cylindrical container made of stainless steel has an internal diameter of 23mm and is 250mm long and was mounted vertically. A metal net in each end acts as a catalyst support. The catalyst temperature was monitored directly under the net in the low end. After passing the SDDS gases were cooled and sampled.

Fig. 3. Experimental set-up of the SDDS and location of coupling point to the Umea reactor

3.3The catalyst

The catalyst, originally developed for the SDS for use together with ammonia (NH3) by CRI Catalyst Company, is a titanium dioxide/vanadium pentoxide type extrudate of 3 – 6mm length and 1.0 – 1.6mm diameter. This allows ready diffusion of target molecules to the high internal surface area giving very high intrinsic activity and removal efficiency at operating temperatures up to 350°C. The amount of catalyst used in the experiments was either 12 or 60 g yielding a gas hour space velocity (GHSV) of 8,000 or 40,000 with a constant flow of 8 liter/min.

3.4Experiment plan

The removal and destruction efficiencies of PCDD/Fhave been determined in six independent experiments byanalyzing the flue gas before the reactor (RAW), afterthe reactor (CLEAN) and on the catalyst (CAT), seeTable 2. They were performed on separate days andnumbered chronologically. Experiments 1, 2 and 6 wereconducted iso-thermally with catalyst temperatures230°C, 150°C and 100°C, respectively, at the lower spacevelocity (8,000 hr-1), whereas experiments 5, 4 and 3represent the same temperature sequence but at 40,000 hr-1. In addition various related compounds, i.e., PCP,PCBz, polychlorobiphenyls (PCBs) and PAHs, have alsobeen determined in the experiments 3–6, thus makingsome efficiency calculations impossible (denoted “–”inTables 2 and 3).

Table 2. Level of PCDD/F expressed as toxic equivalences[I-TEQ] after, before and in the catalyst

Name / Catalyst temperature
(°C) / GSHV
(hr-1) / CLEAN
(after catalyst)
(ng/Nm3) / Raw
(before catalyst)
(ng/Nm3) / CAT
(catalyst)
(ng/Nm3) / Measured
Catalyst temperature(°C)
EXP 1
EXP 2
EXP 3
EXP 4
EXP 5
EXP 6 / 230
150
100
150
230
100 / 8,000
8,000
40,000
40,000
40,000
8,000 / 0.03
0.13
10.00
1.50
0.93
0.36 / 286a
55
61
115
78
172 / -
0.05
89.00
9.30
0.05
2.50 / 223
152
96
148
228
101

aExp 1 was sampled before the last filter, possibly yielding a high value in this case due to the particle bound PCDD/F included.

Table 3. Efficiency of the different organic compounds analyzed

Name / Catalyst temp. / GHSV / PCDD/F
(%) / PCB
(%) / PCB DIN
(%) / PAH
(%) / PCBz
(%) / PCPh
(%)
Removal Efficiency
Exp 3
Exp 4
Exp 5
Exp 6 / 100
150
230
100 / 40,000
40,000
40,000
8,000 / 82.1
98.6
98.8
99.7 / 31.6
84.8
93.9
96.9 / 64.7
93.2
92.1
98.8 / 75.0
88.2
95.2
95.3 / NRa
23.1
32.5
86.3 / NR
76.6
98.0
99.6
Adsorption Efficiency
Exp 3
Exp 4
Exp 5
Exp 6 / 100
150
230
100 / 40,000
40,000
40,000
8,000 / 100.0
6.1
0.1
1.1 / 100.0
39.0
18.0
- / 100.0
100.0
100.0
- / 19.0
0.6
0.1
- / -
0.9
0.3
- / -
0.1
0.2
-
Destruction Efficiency
Exp 3
Exp 4
Exp 5
Exp 6 / 100
150
230
100 / 40,000
40,000
40,000
8,000 / NDb
92.5
98.7
98.6 / ND
46.0
76.0
- / ND
ND
ND
- / 56.0
87.6
95.1
- / ND
22.3
32.2
- / ND
76.5
97.8
-

aNR – No removal bND – No destruction

Samples taken after the catalyst (CLEAN) correspondto emissions to the atmosphere. Samples of filteredraw gas (RAW) were taken in parallel to the above(CLEAN) before the catalyst reactor, except in experiment2 when it was taken at the exact same location butbefore in time with an empty SDDS. In experiment 1,the raw gas sample was taken before the last filter andNH3-inlet. In experiments 1 and 2, NH3 was added tothe gas stream. The ammonia is added to enable simultaneousremoval of NOx. Its effect on dioxin removalis not likely to be significant. The catalyst itself was replacedbetween experiments and these samples weredenoted as “CAT”.

The incinerator was run under normal operatingconditions with high combustion efficiency, seeTable 1. The gases entering the SDDS reactor are notparticle free, the residual fine dust escaping up-stream filters has not been separated from the catalyst material(and would be expected to have contributed tolevels found in the catalyst samples, leading to anoverestimation of the adsorption to an unknownextent).

3.5Sampling

The side stream ended going through the dioxinsamplers, each sample has been collected for approximately2 h (~1 Nm3 of gas). The cooled probe techniquewas used, where the gases are first quenched to < 20°C;this is followed by a two-stage condensation impugnersystem with water and ethylene glycol, respectively, inthe flasks. Finally, there is a polyurethane foam adsorbent (PUF) and an aerosol filter and a second PUF as aprecaution (Fangmark et al., 1990; Marklund et al.,1992). The sampler is approved by the CEN (the standardizingcommittee of the European Union) for dioxinanalysis. It also works well for the related compoundsanalyzed: PCBs, PAHs, PCBz and PCP.

3.6Calculation

The efficiency estimates expressed as percentageshave been calculated as follows:

Removal,R = (1－[CLEAN]/[RAW])*100

Adsorption,A = ([CAT]/[RAW])*100

Destruction,D = (1－([CLEAN]＋[CAT])/[RAW])*100

4.Description of the processes

Performance data were collected from a full scale (200MT per day) waste incinerator at the Heeren municipal waste incineration plant in Roosendaal, the Netherlands. The data was collected, independently, by TAUW, a Dutch company with wide experience of in the field of dioxin sampling and measurement, licensed by the Dutch authorities to carry out statutory dioxin measurement.

Fig 3. Schematic process for the treatment of the Heeren waste incinerator flue gas

It was shown that the Shell DeNOx & Dioxin Destruction System, while converting NOx to below 70ppm, destroyed dioxins at a temperature 245°C from 32 ng[TEQ]/Nm3 down to below the European Union emission norm of 0.1 ng[TEQ]/Nm3. In other words a 99.98% destruction of dioxins was achieved. Sampling of the catalyst demonstrated that even after a significant operating period no dioxins are adsorbed on the catalyst.

5.Performance and economical efficiency

The performances of the SDDS, included the experiment of Umea university and the Heeren MWI plant, are as below:

Table 4. The summary of the performance of the SDDS

Performance / Temperature
°C / Dioxin at outlet,
ng[TEQ]/Nm3 / Dioxin destruction
%
Sweden, University of Umea / 230 / < 0.03 / 99.99
Japan, 300MT per day incineration plant / 170 / < 0.01 / 99.9+
The Netherlands, Heeren incineration plant / 245 / < 0.10 / 99.98

And the many commercial plants, which referred next chapter, proved that the SDDS as well as the SDS have been successfully applied for NOx and dioxins - either individually or simultaneously.

The LFR configuration of the SDSeliminates most constraints with respect to catalyst mechanical strength; as such,the intrinsic activity of the Shell DeNOx catalyst exceeds that of conventional SCRcatalysts resulting in significantly reduced catalyst volumes for equivalent NOxreduction loads, as shown in Fig. 4.

Fig 4. Sell DeNOx system vs. Honeycomb catalyst volume requirement at a temperature 350°C

The SDS has been designed to work in low dustenvironment(typically 10 mg/Nm3) and with low to medium SOx levels. (e.g. waste incinerators with DeSOx and dust removal).

6.Application records

The SDS is applied to flue gas streams originating from gas turbines, co-generation units, gas fired heaters and boilers, ethylene cracking furnaces, chemical industry (nitric acid, caprolactam) and the waste incineration industry.

Table 5. The reference of the SDS

Location / Application / Gas Flow
Nm3/hr / Temperature
°C / Conversion
%
The Netherlands / Waste incineratora / 65,000 / 220 / > 85
Los Angeles / Refinery Heater / 30,000 / 200 / > 99
The Netherlands / Caprolactam / 40,000 / 260 / > 98
Korea / Caprolactam / 40,000 / 260 / > 98
Korea / Caprolactam / 45,000 / 260 / >98
Germany / Caprolactam / 35,000 / 260 / >98
The Netherlands / Gasmotor / 2,000 / 120 / >80
Austria / Gasmotor / 3,000 / 260 / >80
Belgium / Catalyst Plant / 20,000 / 220 / >99.5
California / Catalyst Plant / 30,000 / 220 / >99.5
Germany / Ethylene Cracker / 350,000 / 150 / >80
Location / Application / Gas Flow
Nm3/hr / Temperature
°C / Conversion
%
Germany / Ethylene Cracker / 55,000 / 160 / >80
South Africa / Nitric Acid Plant / 80,000 / 180 / >90
Europe / Nitric Acid Plant / 30,000 / 170 / >85
USA / Nitric Acid Plant / 30,000 / 170 / >85
San Francisco / Gas Turbines / 250,000 / 190 / >90
San Francisco / Gas Turbines / 400,000 / 190 / >90
Gulf Coast / Gas Turbines / 50,000 / 180 / >90
San Francisco / Gas Turbines / 350,000 / 190 / >98
The Netherlands / Gas Turbines / 275,000 / 170 / >90

aThis is the combined SDS and SDDS

The SDDS is mostly applied to flue gas streams originated from the chemical, industrial and municipal waste incinerators. Since 1996, CRI has sold many commercial SDDS plants in Europe, Japan and USA – Where dioxin regulations are more stringent and strongly enforced.

Table 6. The reference of the SDDS

Location / Application / Gas Flow
Nm3/hr / Temperature
°C / DXN in
ngTEQ/Nm3 / DXN out
ngTEQ/Nm3
Ireland / Pharmaceutical waste inin. / 39,000 / 255-275 / 10 design / <0.1 design
UK / Pyrolysis / Gasification / 6,875 / 200
The Netherlands / Industrial waste incin. / 24,000 / 163 / 0.66 actual / 0.011 actual
Japan / 11,000
13,000
12,000
14,000 / 184
182
191
192 / 5.8
4.4
3.3
1.0 / 0.070
0.035
0.046
0.029
Italy / Hazardous waste incin. / 5,400 / 150-165
Japan / Municipal waste incin. / 100,000 / 170 / 0.2 design / <0.1 design
<0.001 actual
Japan / RDF / 20,000 / 220 / 5 / <0.1 design
Japan / MWI with gasification / 27,600 / 210 / 0.1 design / <0.01 design
Belgium / Wood/biomass incin. / 20,000 / 170 / 2.2-5.5 / <0.01
Japan / MSW / 40,000 / 180 / 10 design / <0.1 design
Japan / Industrial waste incin. / 69,000 / 180 / 5 design / <0.1 design
The Netherlands / MWIa / 65,000 / 240 / 2-3 design / <0.01 actual

aThis is the combined SDS and SDDS

7.The history and introduction of company

CRI International, Inc., a member of the Royal Dutch/Shell group of companies, has 8 affiliates. They are all handle the petrochemical and environment catalyst, which from catalyst designing and manufacturing to catalyst regeneration and metal recovery. CRI Catalyst Company handle environment catalyst.

1

Dr. H. S. TANG

EDUCATION

M.B.A (1998), with Honours, Saint Mary's College, Moraga, California, USA

Ph.D. (1980), M.S.E. (1978), in Chemical Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, USA

B.S. (1975), Summa cum laude in Chemical Engineering, Texas A&M University, College Station, Texas, USA

PROFESSIONAL EXPERIENCE

2000-Present: BUSINESS MANAGER – ENVIRONMENTAL CATALYSTS AND SYSTEMS - CRI ASIA PACIFIC PTE LTD., SINGAPORE

1998-1999: TECHNICAL SERVICE MANAGER – ETHYLENE OXIDE CATALYST - CRI ASIA PACIFIC PTE LTD., SINGAPORE

1993-1997: PROJECT MANAGER FOR FEDERAL AND CALIFORNIA CLEAN AIR ACTS COMPLIANCE - SHELL OIL COMPANY REFINERY AT MARTINEZ, CALIFORNIA, USA

1991-1993: ENGINEERING MANAGER FOR REFINERY OPERATIONS - SHELL OIL COMPANY REFINERY AT MARTINEZ, USA

1988-1991:GROUP LEADER FOR COMBUSTION AND REACTION ENGINEERING DEPARTMENT - SHELL WESTHOLLOW TECHNOLOGY CENTER, HOUSTON, TEXAS, USA

1987-1988: SENIOR EXCHANGE SCIENTIST - SHELL RESEARCH B.V., KONINKLIJKE-SHELL LABORATORIUM, AMSTERDAM, THE NETHERLANDS

1980-1987: RESEARCH/SENIOR RESEARCH ENGINEER – CHEMICAL ENGINEERING DEPARTMENT - SHELL WESTHOLLOW RESEARCH CENTER, HOUSTON, TEXAS, USA.

PERSONAL

Naturalized U.S. Citizen went to the U.S. from Hong Kong in 1972 and return to Asia - Singapore 1998

1