DELVELOMENT AND EVALUATION OF NON-CARBON SORBENTS. Executive Summary

Transcription

1 DELVELOMENT AND EVALUATION OF NON-CARBON SORBENTS WESTERN RESEARCH INSTITUTE AND NOVINDA CORPORATION Executive Summary Western Research Institute (WRI) and its cspnsr Nvinda Crpratin (the Cmpany was riginally knwn as Amended Silicates, Inc.) prpsed the develpment, characterizatin and testing f srbents based n clay depsits abundant in Wyming fr the in-flight capture f mercury in pulverized cal derived flue gasses. As a part f the State f Wyming s Clean Cal Technlgies Research Prgram, a tw-year srbent develpment and testing prgram was successfully cncluded such that Amended Silicates is nw a patented, cmmercially available mercury remval srbent. Amended Silicates is the first nn-carbn reagent which preserves fly ash use in cncrete. Amended Silicates ffers ecnmic and envirnmental advantages nt available with ther mercury remval prducts. Backgrund Because f escalating cncern ver mercury emissins frm cal cmbustin the US Envirnmental Prtectin Agency (EPA) has issued stringent mercury emissins standards. The EPA's Maximum Achievable Cntrl Technlgy (MACT) standards and new Mercury and Air Txic Standards (MATS) apply t every cal-fired pwer plant in the cuntry, including the cncrete industry and industrial pwer plants, as well as utilities. The EPA has established an aggressive timeline fr cmpliance with the federal standards: Utility MATS: April 16, 2015 Prtland Cement MACT: September 9, 2015 Industrial Biler MACT Cmpliance deadlines fr majr bilers and Cmmercial/Industrial Slid Waste Incineratrs units will be in 2016 and 2018, respectively. The mst effective methd fr remving mercury frm cal cmbustin gases is the intrductin f a fine pwder material (srbent) int the gas stream. The srbent interacts with gaseus mercury, remving it frm cal cmbustin gases. Srbent particles cntaining the mercury are then captured in the pwer plant s particulate capture systems. Currently, brminated pwder activated carbn (PAC) is the best available cntrl technlgy (BACT) fr in-flight elemental mercury capture in pulverized cal cmbustin units. With prper installatin and peratin it is capable f capturing abut 90% f the elemental mercury in the flue gas. Hwever, PAC injectin fr mercury emissins cntrl has several drawbacks: 1

2 Injected carbn increases the unburnt carbn cntent f the flyash. This mingling f activated carbn with the fly ash adversely impacts the use f captured fly ash as an additive in cncrete prductin Activated carbn is flammable and stred quantities at a pwer plant pse a safety risk Activated carbns can suffer frm pr perfrmance when used with high sulfur cals. Firing high sulfur cals can result in sulfur trixide (SO 3 ) vapr in the flue gas stream. The SO 3 cmpetes with mercury fr binding sites n the surface f the PAC (r unburned carbn) and limits the effectiveness f the injected carbn. Activated carbn is expensive (apprx. $1500/tn). Prject Descriptin The gal f the prpsed prject was t test varius nn-carbn reagents fr the in-flight capture f elemental mercury against the benchmark perfrmance f brminated PAC in varius pwer plant backpass cnfiguratins. Nvinda were t develp srbent chemistries and test them using bench-scale equipment. Once the mst prmising reagents were identified at bench-scale, they were then tested in the WRI s cmbustin test facility (CTF). In an iterative manner the reagent chemistries were ptimized fr activity and dwnstream capture, and tested cmparatively against cmmercially available PAC. Specific bjectives f the prpsed wrk were: Determine the impact f relevant variables n the srbent perfrmance cal types (mainly PRB frm Eagle Butte cal mine (Rnald Seam) with 2-3 runs with PRB frm Eagle Butte mine (Smith Seam). The difference if sulfur and Hg cntent. injectin rates reactin times injectin lcatins temperature Study prduct frmulatin differences Measure impact f different chemical envirnmental cnstituents such as SO 3, NOx, ammnia Analyze the behavir in different particulate cllectin devices (Baghuse (fabric filter), Electrstatic Precipitatr (ESP), Spray Dryer Absrber (SDA)/Baghuse) The target gal was t meet r exceed 90% mercury capture with a material that is cheaper than the PAC-based srbents. Prcedures/Facilities 2

3 WRI s cal cmbustin test facility (CTF) is a nminal 250,000 Btu/hr balanced-draft system designed t replicate a pulverized cal-fired utility biler. In its present cnfiguratin, the unit is set up t simulate a tangential-fired biler, but may be easily adapted t wall-fired r ther cnfiguratins. The fuel feed system cnsists f screw-based feeders and pneumatic transprt t fur burners inserted in the crners f a refractry-lined firebx. The burners can be angled t attain different tangential flw characteristics in the firebx. The unit is equipped with apprpriately sized heat-recvery surfaces such that the time/temperature prfile f a utility biler is replicated. These surfaces cmprise water-cled panels that simulate the waterwall, an air-cled superheater, reheater, tw ecnmizers and preheater. CTF includes prvisins fr preheating the cmbustin air t mimic a utility air preheater. The system als includes ver-fire air injectin prts fr cmbustin staging. The unit is equipped with tw baghuses fr cntinuus fly ash remval and fr clean sampling under different steady-state peratins. Figure 1. Schematic f the Cal Cmbustin Test Facility with the ESP and the SDA (Recent Upgrades) As a part f this prpsal, CTF was mdified t allw srbent testing in varius back-end plant cnfiguratins such as with baghuse, with ESP, and with SDA/baghuse. As shwn in Figure 1, a spray dry absrber and an ESP were added t the existing CTF layut. These mdificatins f the CTF allwed fr flexibility in cnfiguring the Air Pllutin Cntrl Devices (APCD) t mimic as they are typically set in 3

4 a majrity f the PRB cal-fired pwer plants. This is a very imprtant factr, since mercury reductin levels are knwn t be highly dependent n the APCD installed at the plant. Over the curse f the prject, fifty-fur test runs were cmpleted with nn-carbn based mercury srbents prepared by Nvinda. A ttal f nineteen test runs were cnducted with baghuse, twentyeight runs with ESP (bth in energized and de-energized mdes), and five runs with SDA/baghuse. Tests investigated the effect f flue gas temperature, srbent cmpsitin, and srbent injectin rate n the mercury emissin reductin. In additin variables specific t the APCD in use were als investigated. A typical test included starting the CTF n an auxiliary fuel t warm-up the furnace. It is extremely imprtant that carbn mnxide level during start up and during the test were kept at the lwest pssible level. During cal firing, a high level f carbn mnxide is a sign f frmatin f unburned carbn. T minimize the frmatin f unburned carbn in the fly ash, high temperature in the lwer furnace and sufficient excess xygen are required. After a sufficient warm-up, and when the desired exit temperature frm the APCD was satisfied, cal feed was started while maintaining the excess xygen in the lwer furnace at 5% xygen. CTF was perated n cal fr fur t six hurs t achieve steady state. Mercury measurements were then made t establish base-line mercury cncentratin in the flue gas. Fr the PRB cal used fr all the tests cncluded under this prject the uncntrlled mercury cncentratin was expected t be in the 9-10 µg/nm3 range. Srbent injectin was started at the desired rate while cntinuusly mnitring the mercury cntent f the gases leaving APCD cnfiguratin. A typical srbent injectin test was abut 90 minutes lng Hg, micrgram/nm :00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 Time f Day Figure 2. Typical srbent tests run data Figure 2 shws a typical test run data fr mercury srbent test. The figure shws the mercury cncentratin in the cmbustin gases as a functin f time-f-day. Black symbls represent the 4

5 mercury cncentratin in the cmbustin gases when n srbent is being injected and thereby represent baseline mercury cncentratin. Fr example, arund 2:00 PM n that test day the mercury cncentratin in the flue gas was just belw 9 micrgram/nm3. Red symbls represent the mercury cncentratin when srbent injectin has been started. The figure shws tw such time perids fr tw different srbent injectin rates. Clearly, irrespective f the injectin rate, mercury cncentratin in the cmbustin gases begins t decrease as sn as the srbent injectin is started and within minutes reach a cnsiderably lwer value. In the graph displayed in Figure 2 this value arund 9:00 PM is less than 0.5 micrgram/nm3, representing a better than 90% reductin in mercury cncentratin. Frm several similar test runs with several different srbent chemistries it was established that indeed nn-carbn srbents can achieve mercury emissins reductin cmparable r better that thse pssible with brminated activated carbns. Figure 3 cmpiles data frm several nn-carbn srbent tests at different injectin rates, and cmpares them with activated carbn data. Clearly, perfrmance f the nn-carbn chemistries is quite cmparable with that f cnventinal and treated pwder activated carbns % Mercury Remval (% f ttal Hg cntent) 90.0% 80.0% 70.0% 60.0% resulting Amended Silicates srbent perfrmance envelpe in a pulse jet system. 50.0% 40.0% Injectin Rate (lbs/mmacf) Amended Silicates Cnventinal PAC Treated PAC Figure 3. Mercury remval as a functin f srbent injectin rate fr baghuse plant cnfiguratin Please nte that the data presented in figure 3 are fr the plant cnfiguratin emplying a baghuse. Similar results were als btained in plant cnfiguratins with spray dryer absrber with a baghuse. The perfrmance f the nn-carbn srbent was similarly cmparable t cnventinal PAC in an ESP set-up. 5

6 Flyash samples cllected during these tests were subjected t Txicity Characteristic Leaching Prcedure (TCLP). TCLP is designed t determine the mbility f elements and cmpunds in liquid and slid waste byprducts. Tests have shwn the mercury captured by Amended Silicates t be extremely stable. Testing cnducted elsewhere have shwn that Amended Silicates is 100% cmpatible with fly ash use in cncrete prducts. By using Amended Silicates fr mercury cntrl, utilities enjy the dual benefits f preserving the beneficial use and value f fly ash as a prtland cement replacement, while aviding csts assciated with landfill dispsal. The U.S. Department f Energy s Natinal Energy Technlgy Labratry (DOE/NETL) estimates the beneficial use value f cal fly ash t be $18/tn, while landfill csts are estimated t be $17/tn. This indicates a net benefit f $35/tn f fly ash t a plant selling its ash as a prtland cement replacement simply by adpting Amended Silicates fr mercury emissin cntrl. Cnclusins As a part f the State f Wyming s Clean Cal Technlgies Research Prgram, a tw-year srbent develpment and testing prgram was successfully cncluded. Nvinda Crpratin has develped nn-carbn mercury srbent fr the in-flight capture f mercury in pulverized cal derived flue gasses. Amended Silicates is the first nn-carbn reagent which preserves fly ash use in cncrete. Amended Silicates ffers ecnmic and envirnmental advantages nt available with ther mercury remval prducts. In tests cncluded under this prject, Amended Silicates achieved mercury remval cmparable t cnventinal PAC With respect t impact f flue gas chemical envirnment, Amended Silicates perfrmance was similar t cnventinal PAC with respect t nt affected by flue gas chemical envirnment 6