분무형 스크러버에 내에서 액적크기에 따른 물질전달에 관한 전산해석적 연구

The Numerical Study on Effect of the Droplet Sizes on Internal Mass Transfer in the Spray Type Scrubber

Abstract

여러 국가를 통행하는 다양한 형태의 선박에서 배출되는 황산화물에 의해 지역적인 대기오염이 심화됨에 따라 국제해사기구에서는 황산화물 배출제어지역을 설정하여 규제하고 있다. 이러한 지역적 규제를 만족시키기 위해서는 선박의 연료선택방법과 배가스 후처리 장치가 적용되고 있으나 경제적인 이유로 스크러버를 설치하여 배출되는 황산화물의 양을 저감하는 배가스 후처리 방법이 주로 선호되고 있다. 스크러버는 배출가스 중 황산화물을 액적에 흡수시켜 황산화물의 양을 저감하는 장치로 액적의 크기에 따라 스크러버의 성능이 좌우된다. 이러한 성능을 평가하기 위해서, 본 논문에서는 대향류형 스크러버와 사이클론 스크러버를 설계하고, 전산유체역학을 이용하여 각 액적의 크기에 따른 탈황 효율과 액적이 증발되는 양을 평가하였다. 평가 방법으로 스크러버 내부는 기체와 액체의 2상 유동을 가지기 때문에, Eulerian-Eulerian 해석 기법을 사용하였으며, 액적의 직경이 $100{\mu}m$, $300{\mu}m$, $500{\mu}m$와 $700{\mu}m$일 때 계산을 진행하여 스크러버를 분석하였다. 계산 결과, 2종류의 스크러버 모두 $500{\mu}m$와 $700{\mu}m$일 때 높은 탈황 효율과 낮은 증발량을 나타내었다.

As regional air pollution gets worse by the sulfur oxides emitted from various types of vessels passing through the many countries, the International Maritime Organization establishes the emission control areas and regulates sulfur dioxide in those areas. In order to satisfy these regional regulations, the fuel selection method and the exhaust gas post-treatment device are applied to the ships. Due to the economic reasons, the post-treatment method of exhaust gas for reducing the amount of sulfur oxides discharged is mainly preferred. The scrubber which is dominantly used in the ships are the spray type system where the sprayed liquid drops used for capturing the soluble sulfur dioxides in the exhaust gas. The performance of the spray type system depends on the size distribution of the sprayed droplets. In order to evaluate this performance, we designed counterflow type scrubber and cyclone scrubber and evaluated the desulfurization efficiency and the amount of droplet evaporation according to the size of each droplet by using computational fluid dynamics. The Eulerian-Eulerian analysis method was used because the scrubber had a gas-liquid two-phase flow inside the scrubber. When the diameter of the droplet was $100{\mu}m$, $300{\mu}m$, $500{\mu}m$ and $700{\mu}m$. As a result, both of scrubbers showed high desulfurization efficiency and low evaporation amount at $500{\mu}m$ and $700{\mu}m$.

Figure 2. Fuel oil sulfur limits.

Figure 1. SO_x emission control areas.

Figure 3. Schematic of counterflow scrubber.

Figure 4. Schematic of cyclone scrubber.

Figure 5. Notation of scrubber.

Figure 6. Boundary conditions.

Figure 7. Comparison of CFD data and experimental data [19].

Figure 8. Comparison of CFD data and experimental data [12].

Figure 9. Results plane of counterflow scrubber.

Figure 10. Results plane of cyclone scrubber.

Figure 11. Results line of counterflow scrubber.

Figure 12. Results line of cyclone scrubber.

Figure 13. Velocity distribution of counterflow scrubber.

Figure 14. Gas streamlines of counterflow scrubber.

Figure 15. Velocity distribution of cyclone scrubber.

Figure 16. Gas streamlines of cyclone scrubber.

Figure 17. Gas velocity distribution of counterflow scrubber.

Figure 18. Droplet velocity distribution of counterflow scrubber.

Figure 19. SO₂ mass fraction distribution of counterflow scrubber.

Figure 21. Droplet velocity distribution of cyclone scrubber.

Figure 20. Gas velocity distribution of cyclone scrubber.

Figure 22. SO₂ mass fraction distribution of cyclone scrubber.

Figure 23. Gas velocity distribution of counterflow scrubber.

Figure 25. Temperature distribution of counterflow scrubber.

Figure 27. Droplet velocity distribution of cyclone scrubber.

Figure 24. Droplet velocity distribution of counterflow scrubber.

Figure 26. Gas velocity distribution of cyclone scrubber.

Figure 28. Temperature distribution of cyclone scrubber.

Table 1. Wet scrubber principal dimensions by engine power

Table 2. Fuel oil sulphur limits recorded and corresponding emissions values

Table 3. Some literature using computational fluid dynamics

Table 4. Comparison of desulfurization efficiency of each scrubber

Table 5. Comparison of interphase mass transfer rate of each scrubber