Desulfurization of Flue Gas
Matthew Allsopp, Mallory Clites, Christopher Nunes, Charles Onyenemezu

CHBE 446

February 6, 2014

Outline
● Introduction ● Regulations on Sulfur Dioxide ● Flue-Gas Desulfurization Methods ○ Scrubbers ○ SNOX ○ Wet Sulfuric Acid Process ● Application to Project

Introduction
● Flue-Gas Desulfurization (Post-Processing) ○ Removes sulfur dioxide from flue gas emissions (often chemically) ● Flue Gas ○ The effluent stream of a process; composed of a mixture of gases ○ Some products formed from combustion reactions: ■ Carbon Dioxide, Carbon Monoxide, Water Vapor ■ Sulfur Dioxide, Hydrogen Sulfide ○ Other products are non-reactive species ■ Nitrogen

Introduction
● Sulfur Dioxide
○ 93% of SO2 emissions arise from fossil-fuel combustion at power plants or other industrial facilities

● Issues with SO2

○ causes respiratory problems ○ air pollutant ○ reactive acid ■ oxidizes to form H2SO4

"Sulfur Dioxide." EPA. Environmental Protection Agency, 08 Jan. 2014. Web. 03 Feb. 2014.

Regulations on Sulfur Dioxide
● Natural atmospheric concentration is 1ppb ● Two standards of differing tolerance ○ Primary- stricter to protect elderly, children ■ Level averaged over 3 years must not exceed 75 ppb. ○ Secondary- to protect public welfare (plants, animals) ■ Must not exceed 0.5 ppm more than once per year ● These numbers for the basis for the design of a power plant
Owen, Lewis A.; Pickering, Kevin T (1997). An Introduction to Global Environmental Issues. Taylor & Francis. pp. 33–. ISBN 978-0-203-97400-1. "US Environmental Protection Agency." EPA. Environmental Protection Agency, n.d. Web. 01 Feb. 2014. CaCO3 (s) +CO2 (g)

○ ● ●

Lime Slurry
Ca(OH)2 (s) +SO2 (g) -> CaSO3 (s) +H2O (l)

Mist eliminator entrains excess slurry liquid 85% of all scrubbers are wet scrubbers in the United States

Lesson 9: Flue Gas Desulfurization (Acid Gas Removal) Systems. Yosemite EPA(n.d.): n. pag. EPA. Web. 2 Feb. 2014.

Wet Scrubber Process
Advantages ● ● ● ● Relatively high removal efficiency (90-95%) Low cost of operation Minimal safety hazardous (explosions, fires) Collects both gas and particulate matter

Disadvantages ● ● ● Wet waste production (contaminated scrubber liquid) Formation of highly corrosive acids High power requirements

Semrau, K. T. 1977. Practical process design of particulate scrubbers. Chemical Engineering. 84:87-91.

Dry and Semi-dry Scrubbing
● Uses quicklime (CaO) to remove pollutants rather than saturating flue gas with moisture
CaO(s) +SO2 (g) -> CaS (s) + 1.5O2

●

● ●

Produces solid salt waste (CaS) ○ minimal hazard ○ less requirements for disposal Does not produce corrosive material or waste water ○ Less maintenance and disposal costs Less overall efficiency than wet scrubbing

Lesson 9: Flue Gas Desulfurization (Acid Gas Removal) Systems. Yosemite EPA(n.d.): n. pag. EPA. Web. 2 Feb. 2014.

Dry and Semi-dry Scrubbing
Spray Drying (Semi-dry) ● the quicklime sorbent contains a slight amount of water that will remain as vapor within flue gas at end of process sprays a quicklime slurry into the flue gas 12% of all scrubbers used in the US at least 70% efficiency, higher in recent years
Dry Flue Gas Desulfurization. Integrated Solutions for a Clean Environment. Hamon Research - Cottrell, Inc., n.d. Web. 2 Feb. 2014.

● ● ●

Lesson 9: Flue Gas Desulfurization (Acid Gas Removal) Systems. Yosemite EPA(n.d.): n. pag. EPA. Web. 2 Feb. 2014.

Dry and Semi-dry Scrubbers
Dry Sorbent injection ● entirely dry quicklime sorbent is sent into the flue gas 3% of all scrubbers used in the US upwards of 70% efficiency, not as high as wet or semi-dry scrubbing

● ●

Dry Sorbent Injection May Serve as a Key Pollution Control Technology at Power Plants. Today in Energy. U.S. Energy Information Administration, n.d. Web. 04 Feb. 2014.

SNOX
● Sulfur Dioxide is oxidized at high temperature on Vanadium oxide catalyst ● NOx reduced to N2 in catalytic converter ● SO2+ O2⇔ SO3+ H2SO4 ● Sulfur Trioxide converted to commercial grade Sulfuric acid ● Environmentally friendly
○ ○ ○ Produces steam instead of waste water NOx (NO and NO2) also reduced to N2 NOx are a dangerous pollutant

"GCSE CHEMISTRY - The Reaction of Sulfur Dioxide with Oxygen to Make Sulfur Trioxide for The Contact Process to Make Sulfuric Acid - GCSE SCIENCE." GCSE CHEMISTRY - The Reaction of Sulfur Dioxide with Oxygen to Make Sulfur Trioxide for The Contact Process to Make Sulfuric Acid - GCSE SCIENCE.N.p., n.d. Web. 05 Feb. 2014.

Wet Sulfuric Acid Process (WSA)
Same as SNOX but without nitrogen processing

"File:WetSulfuricAcidProcessDiagram.svg." Wikipedia. Wikimedia Foundation, 22 Jan. 2014. Web. 05 Feb. 2014.

Application to Project
● Claus process produces residual sulfur dioxide
○ ○ ○ ○ ○ ○ Intermediary Reaction Final Reaction Residual H2S could also be sent to scrubber Wet scrubbers are most efficient Dry scrubbers do not produce waste streams ■ salt needs to be sent to landfill SNOX process most energy-efficient method ■ produces commercial sulfuric acid (H2SO4) ■ does not produce waste products or waste water ■ ideal for processes at elevated temperatures (NO2)

● Wet, dry scrubbers and SNOX all potential methods

Block Flow Diagram (SNOX)

"SNOX Process." Wikipedia. Wikimedia Foundation, 20 May 2013. Web. 05 Feb. 2014. .

Questions?