Water Scrubbing Technology for reducing marine emissions

Transcription

1 Water Scrubbing Technology for reducing marine emissions Dennis Y.C. Leung & Gabriel C.K. Lam Dept. of Mechanical Engineering The University of Hong Kong

2 Background Hong Kong is one of the busiest ports in the world and suffering from serious air pollution due to the emissions from ships including ferries, barges, and ocean going vessels. Most of the ships (particularly those cruise ships and ocean going vessels) still use poor quality high sulphur fuels producing enormous amount of SO 2 and dark smoke.

3 Background (cont d) Marine vessels emissions have been increasing over the past decades and become the top emitter of SO 2, RSP and NOx in HK.

4 Source: EPD website 4

5 Background (cont d) In recent years the government started to look into ways to improve the emissions from marine sources. e.g. H.K. has just legislated on the use of low sulphur diesel (<0.05%) in April 204 under the APC (Marine Light Diesel) Regulation. A desk top study has been conducted by HKU in 2008 on the effectiveness of various APC control methodologies for marine applications. It was found that wet scrubbing technology is a low cost and effective technology that is suitable for ferry fleet in Hong Kong.

6 Principle of wet scrubbing Clean air Absorbing liquid a basic chem. engg. unit operation usually carried out in a column or tower in which the gas to be cleaned comes into contact with fresh liquid introduced at the top; Gas Commonly used nowadays for absorption of air pollutants (e.g. FGD in HEC and CLP)

7 Background (cont d) The pollutant removal effectiveness of the scrubbing technology in marine application will be the same, if not better than the common measures of reducing fuel S or installing other exhaust after-treatment devices such as diesel oxidation catalysts and particulate filters. Subsequently, a seawater scrubber has been designed, installed and tested in a ferry (Star Ferry) with 6 x 60 kw engines.

8 Characteristics of Star Ferry fleet Using Crossley 2-stroke marine diesel engine Provide steady propulsion even at low rpm Low rpm(from rpm to 340 rpm max) Low fuel consumption: ~4 litre/km. Low exhaust gas temperature (<70 ) Have tried other fuels such as ULSD, emulsified fuel but the effects are not satisfactory Very congested engine room

9 Testing results on using other fuels Low S* diesel ULSD* Emulsified* Fuel SO 2 (g/kw-hr) Smoke (HSU) Av Cruise Max Particulate (g/kw-hr) * Results from previous studies of Star Ferry

10 Wet-scrubber installed

11 Wet scrubber in operation

12 Testing results on using other fuels and scrubber alone Low S* diesel ULSD* Emulsified* Fuel Seawater Scrubber SO 2 (g/kw-hr) Smoke (HSU) Av Cruise Max >70% for max Particulate (g/kw-hr) NOx (g/kw-hr) * Results from previous studies of Star Ferry

13 Comparison between flumes with and without the wet scrubber With scrubber Without scrubber

14 Background (cont d) The scrubber was found to be very efficient in removing air pollutants from the exhaust gas, in particular, a reduction in dark smoke of ~70%, SO 2 ~90%, and unburnt HC ~40% can be achieved. Despite the system is very effective in removing SO 2 and dark smoke, it has very little effect on NOx in the exhaust gas due to the poor solubility of NO in seawater. NOx is a pollutant very difficult to be removed or reduced due to its complicated formation mechanism (prompt, thermal and fuel NOx).

15 Background (cont d) There are 3 sources of NO x during a combusting process:-. Thermal NO x : oxidation of atmo. molecular N 2 at high temp. 2. Prompt NO x : rapid oxidation of atmo. nitrogen in the presence of HC radicals (generally insignificant) 3. Fuel NO x : Direct conversion of fuel bound nitrogen

16 Background (cont d) Conventional ways of removing NOx from exhaust include post-combustion control and exhaust gas treatment. Post-combustion control mainly modifies the combustion chamber/burners to reduce the peak combustion temperaturemainly incorporated in modern boilers and engines Exhaust gas treatment is more flexible and mostly used to further reduced the NOx from boilers and engines. Exhaust gas treatment technologies for NOx reduction include: Selective catalytic reduction (SCR) and absorption (NO 2 only).

17 High in capital and running cost SCR technology for NOx reduction Commonly used for stationary sources (e.g. Town Gas & CLP) and new vehicles (Euro 5 & beyond) Normal efficiency 50-90% Need a higher exhaust gas temperature (>200 ) Need to store urea on board

18 Wet scrubbing technology As mentioned before, the wet scrubbing technology was found to be very efficient in removing dark smoke, SO 2 and HC from the exhaust gas but has very little effect on NOx According to the following equation, NO can be removed by first oxidized to NO 2 and then removed by water: NO + O 3 NO 2 +O 2 2NO 2 + H 2 O + 0.5O 2 2HNO 3 Feasibility of further NOx removal in the scrubber previously developed has been pursued by additional of O 3 as the oxidation agent.

19 Laboratory setup for testing the De-NOx system vertical and single nozzle

20 Laboratory setup for testing the de-nox system- horizontal and multi-nozzle

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22 Main scrubber design L/G ~6.6 (mass) 22

23 Ozone generator (380V, 3ph, 50Hz) 23

24 Monitoring/measurement equipment 24

25 Measured Fuel Flow to Engine Data set Measured Average for Average for (L/min.) 6 60kW 3 60kW (L/min.) (kg/h)* (kg/h)

26 Measured O 2 Content and Calculated Gas Flows at Scrubber Inlet Engine Speed (rpm) Data set Measured O 2 (%) Average O 2 (%) Dry Basis Gas Flow (Nm 3 /kg fuel) Wet Basis Gas Flow (Nm 3 /kg 0 o C, Wet Basis Gas Flow (Nm 3 0 o C, atm. atm

27 Ozone Generator Output Data set Engine speed (rpm) Ozone Generator Manual Output % Ozone Generator flow rate from rotameter (m 3 20 o C Ozone Generator rotameter pressure (MPa) Ozone Generator gas flow rate (Nm 3 /h) Ozone Output Conc. by Teledyne 465H (g/nm 3 ) Calculated Ozone Output (g/h)

28 Dilution and Mixed Ozone Concentration at Scrubber Inlet due to the Main Ozone Generator Output Data set Engine speed (rpm) 300 Main Ozone Generator ozone output (g/h) 978. Small Ozone Generator ozone output (g/h) 4.9 Main Ozone Generator gas flow rate (Nm 3 /h) Engine exhaust gas flow rate (Nm 3 /h) Deduced Dilution to Engine Exhaust Gas Calculated Ozone Conc. at scrubber inlet (ppm) % % % % % % % % % 465.9

29 NO and NOx reduction (dry basis) Data set Engine Speed (rpm) Scrubber Inlet (ppm) Scrubber Outlet (ppm) Removal efficiency (%) NO NOx NO NO * 2 NOx NO NOx % 3.8% % 7.0% % 24.% % 43.2% % 44.% % 62.9% % 35.5% % 65.%

30 Other issues of concern 30

31 Effluent discharge Determinand Flow rate (m3/day) 0 ph (ph units) Temperature ( ) Colour (lovibond units) (25mm cell length) Suspended solids BOD COD Oil & Grease Iron Boron Barium Mercury Cadmium Other toxic metals individually Total toxic metals Cyanide Phenols Sulphide Total residual chlorine Total nitrogen Total phosphorus Surfactants (total) E. coli (count/00ml) Table 9b Standards for effluents discharged into the marine waters of Victoria Harbour Water Control Zone (All units in mg/l unless otherwise stated; all figures are upper limits unless otherwise indicated) >0 and >200 and >400 and >600 and >800 and >000 and >500 and >2000 and >3000 and (Enacted 990) >4000 and >5000 and

32 Effluent sampling Background sampling From scrubber outlet 32

33 Water Quality Sampling and Analysis Results Conditions Measured Standard Baseline (Ambient seawater) Temperature o C ph Suspended Solids mg/l <2 200 COD mg/l < O&G mg/l <5 20 Total Nitrogen rpm cruising Temperature o C ph Suspended Solids mg/l COD mg/l < O&G mg/l 6 20 Total Nitrogen rpm cruising Temperature o C ph Suspended Solids mg/l COD mg/l < O&G mg/l <5 20 Total Nitrogen

34 Date IMO Sulphur Limit S Limit in Fuel (% m/m) SOx ECA Global % 4.5% % % % 2020 a 0.5% a - alternative date is 2025, to be decided by a review in 208

35 IMO NOx Emission Limits NOx Limit, g/kwh Tier Date n < n < 2000 n 2000 Tier I n Tier II n Tier III n In NOx Emission Control Areas (Tier II standards apply outside ECAs).

36 Concluding remarks.a water scrubber has been installed and tested in one of the ferries of Star Ferry Co., Ltd. for reducing the air pollutant emissions from its exhaust. 2. The original scrubber is found to be effective in reducing several important pollutants such as dark smoke, SO 2 and hydrocarbon but there is very little effect on NOx. 3. With the installation of an ozone dosing system, the NOx in the exhaust gas can also be reduced with a reduction of ~75% and 65% for NO and NOx respectively at low speed operation mode and ~38% and 35% at high speed operation mode.

37 Concluding remarks (cont d) 4. The performance of the scrubber can be further improved by better design of the mixing chamber and reheater of the scrubber. 5. Higher O 3 injection will also increase the reduction of NOx. 6. The effluent discharge due to the scrubbing was also found to be acceptable to local discharge criteria. 7. Wet scrubbing may provide an alternative solution for reducing the pollutant emissions from marine sources.

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39 Acknowledgement This project is funded and supported by various bodies at 2 stages: The st stage: scrubber without de-nox is funded by Star Ferry Co. Ltd. The 2 nd part: scrubber with de-nox system is funded by the Environment and Conservation Fund (ECF) Star Ferry Co. Ltd. Jockey Club Heavy Duty Vehicle Emission testing Centre Hongkong Electric Co., Ltd. Leung Wan Kee Shipyard Ltd.

40 Project team 40

41 Thank you! 4