AC and Regenerated Coke

The AC is a carbonaceous material produced by steam activation (at ~900 °C). It has high mechanical strength against abrasion and crushing. Its surface area is 150–300 m²/g, less than the conventional activated carbon, but not much higher than the metallurgical coal. AC comes in tablet or almond‐type shape and is generally much larger than the activated carbon. AC is easier to produce and less expensive than activated carbon. Figure 9.15 shows the internal model of AC and its pore structure. Figure 9.16 shows mercury vapor removal efficiency versus time.

Thermal Regeneration of AC

At the temperatures in the regenerator heating section adsorbed sulfuric acid, ammonium sulfate, and ammonium bisulfate are decomposed to SO₂. AC pellets enter via lock hoppers and is in gravity counter‐flow against desorbed gases and N₂ carrier gas. Sulfur‐rich gas containing SO₂, CO₂, N₂, and H₂O exits the regenerator to an acid plant as follows:

(^*denotes adsorbed species; non‐isothermal desorption kinetics reach peak rates at 300 °C and completion by 450 °C).

Performance and Benefits of ReACT^TM

Table 9.3 presents a typical performance at J‐Power EnTech 2x600MW ISOGO coal‐fired power plant in Japan (Reynolds, personal communication). The benefits of the advanced multi‐pollutants control by the ReACT™ can be summarized as follows:

• By‐product revenue – Sulfuric acid is the world’s number one commodity chemical with a market value of $50 200/T. Instead of producing disposal gypsum or fly ash/gypsum waste, ReACT™ produces saleable by‐product.
• Avoided disposal costs – For every ton of SO₂ controlled in conventional flue‐gas desulfurization (FGD), about three tons of solid waste is generated. More if fly ash is part of the FGD waste stream.
• Near zero water use – ReACT™ uses minimal water, in significant contrast to FGD systems. For a 500 MW plant, a WFGD (wet flue gas desulfurization) system would require 275 000 000 gal/year while ReACT™ would use near zero.Figure 9.15 Internal model of AC – pore structure.Figure 9.16 Mercury vapor removal efficiency (%) versus time.Table 9.3 Typical performance of advanced multi‐pollutant removal.PollutantsEmissions permitOperating resultsEfficiency (%)Inlet concentrationOutlet concentrationSO_x10 ppm
  (0.025 lb/MMbtu)>98<410 ppm
  <0.85 lb/MMbtu<1 ppm
  <0.002 lb/MMBtuNO_x13 ppm
  (0.02 lb/MMbtu)10–50<20 ppm
  0.03 lb/MMbtu<7 ppm
  <0.011 lb/MMbtuParticulate5 mg/Nm³
  (0.004 lb/MMbtu)>95
  (>99.9 w/ESPs)<100 mg/Nm³
  <0.1 lb/MMbtu<3 mg/Nm³
  <0.002 lb/MMbtu
  (w/backend ESP)Hg––>902.5 μg/Nm³<0.25 μg/Nm³
• Minimal plant modifications – ReACT™ can flow to the existing stacks with no change in liner materials. ReACT™ is located downstream of existing equipment and does not necessitate modifications to upstream equipment.
• NO_xperformance options – ReACT™ systems may be designed for a range of NO_x reduction options – from co‐benefit levels of 30% through alternative designs reaching 80%.