ENERGY-RECOVERY FROM SOLIDS IN ST. PETERSBURG, FL: BIOGAS TO VEHICLE FUEL AND CHP. Phone:

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1 ENERGY-RECOVERY FROM SOLIDS IN ST. PETERSBURG, FL: BIOGAS TO VEHICLE FUEL AND CHP Jhn L. Willis *, Brwn and Caldwell * JWillis@BrwnCald.cm Phne: ABSTRACT The City f St. Petersburg, FL (City) prduces an average f 41,000 wet tns per year (WTpY) f Class-B bislids and 40,000 WTpY f yard waste. The City perates fur Water Reclamatin Facilities (WRFs): Albert Whitted WRF, NEWRF, NWWRF, and SWWRF. Plans are underway t decmmissin the Albert Whitted WRF and pump that service area s wastewater t the SWWRF fr treatment. The Bislids- and Yard-Waste-t-Energy Feasibility Study (Study) was driven by the State f Flrida s effective ban n Class- B bislids land applicatin (Flrida Administrative Cde Chapter ) and the City s desire t prduce renewable pwer frm currently under-used resurces. During the feasibility study and pst-study ptimizatin, the team (City f St. Petersburg and Brwn and Caldwell staff) investigated ver 35 ptins and determined that an initial phase upgrade culd save the City up t $40 millin ver the next 20 years. The planned upgrades will cnslidate all slids prcessing at the SWWRF thrugh a cmbinatin f sludge frcemains and the existing cllectin system. Add primary clarifiers t catch the cnveyed slids and ther settleable slids at the SWWRF and upgrade the digestin at that plant t Class-A, temperature-phased, anaerbic digestin (TPAD). Digester gas Figure 1: St. Petersburg Service Area and WRF Lcatins wuld be cnverted t vehicle fuel (renewable cmpressed natural gas, rcng) fr the City s sanitatin truck fleet. The prject wuld als include new engines fr prductin f pwer (fueled by either natural gas r treated digester gas) and the heat needed fr Class-A digestin. Additinal thickening and dewatering capacity wuld als be required. NEWRF KEYWORDS Bislids Planning; Renewable Pwer; Vehicle-Fuel Cnversin; Class-A Digestin; Land Applicatin; and Bienergy. INTRODUCTION The City f St. Petersburg prvides wastewater treatment and yard waste cllectin fr ver 315,000 residents. Fur WRFs with service areas shwn in Figure 1 currently prvide the required wastewater treatment. The Albert Whitted WRF will, hwever, be decmmissined and its flw pumped t the SWWRF. The average flws, and waste activated sludge (WAS) and NWWRF AWWRF SWWRF

2 bislids prductin fr each WRF are summarized in Table 1. Surce/WRF WAS Slids (dry lb/d) Bislids (dry lb/d) Flw (mgd) Albert Whitted WRF 7,500 5, The State f Flrida recently prmulgated Flrida Administrative Nrtheast WRF (NEWRF) 11,300 7, Cde Chapter that put new Nrthwest WRF (NWWRF) 18,500 13, requirements n the land applicatin f Class-B bislids. The rule Suthwest WRF (SWWRF) 11,300 7, change takes effect in January f Ttal: 48,600 33, Under the new rules, individual bislids applicatin site Table 1: Annual Mass f WAS and Bislids permits are required with significant site new restrictins and develpment, maintenance, and cnfrmance with nutrient management plans fr nitrgen and phsphrus. Because the additinal cst f cntinued Class-B land applicatin wuld likely increase dramatically under the new rules, The City wanted t investigate alternative beneficial reuse ptins. The feasibility study started in August f 2010 and included fur wrkshps and fur technical memranda (TM) as deliverables. The prject executin was fluid and new ptins were investigated and additinal analyses perfrmed as warranted answering new questins. The fllwing prblem statement was identified in the first wrkshp and revisited in each subsequent wrkshp: The Slutin must prvide a cst-effective system t prcess sludge and yard waste using reliable, advanced technlgies, cnsidering partnerships and reginal invlvement, with cmmunity input while meeting regulatry and grant requirements. The cmmunity-acceptable slutin will reduce energy expenses, greenhuse gas emissins, and the City s carbn ftprint; benefit rate payers; and prduce renewable energy by incrprating green and sustainable technlgies. The slutin must als be peratinal by January This statement served as a cnsistent reminder f what the study s bjectives were and allwed each new ptin/questin t be cnsidered in this cntext. Figure 2: Feasibility Study Prcess Overview FEASIBILTY STUDY The Feasibility Study tk place in slightly under ne year, spanning frm August f 2010 t July f Figure 2 shws the varius prject activities and linkages between deliverable and grup wrkshp. The City staff was well represented at the meetings with a diverse grup, including: City Public Administratr Wrks City Directr f Engineering and Capital Imprvements

3 Water Resurces Directr Water Resurces Assistant Directr Assistant Engineering Directr Engineering Manager Water Reclamatin Manager Chief Operatr fr each f the fur WRFs Other engineers and peratins specialists. Wrkshp 1 included develpment f the earlier-discussed prblem statement and brainstrming f an initial set f 9 ptins. Between Wrkshps 1 and 2, the ptins list was expanded/refined t include three ther ptins, bringing the ttal reviewed at the secnd wrkshp t 12 ptins. Wrkshp 2 reviewed the mass and energy balances fr 12 ptins and TM1 n prcess lading/basis f design. All mass and energy balances were develped based n current average prductin but that installed facilities must be able t accmmdate the peak-mnth and peak-day slids prductin. The City cnsiders their service area t be built ut and as such, did nt frecast significant increases in slids prductin ver the cnsidered 20-year life f the study. One realizatin made during Wrkshp 2 was that it is extremely difficult t prcess and make determinatins based n wet tns hauled, average megawatts prduced r cnsumed, r cubic feet f natural gas used. While it was apparent that sme ptins had better energy prfiles r resulted in cnsiderably fewer truck trips; it was very difficult t determine hw much better r t nrmalize the relative advantages f cnsidered ptins. It was determined that ecnmics, presented in terms f 20-year present wrth, wuld be develped fr each subsequent ptin s that the relative benefits culd be cmpared based n a unifrm, easily understd metric: dllars. Finally, all f the present-wrth evaluatins were run at average slids prductin cnditins, as ecnmic perfrmance tracks mst clsely with these criteria as ppsed t ther design criteria. Seasnal variatins were checked against the average perfrmance t ensure that winter r summer demands wuld nt result in unfreseen, negative r psitive implicatins. It was als determined at the secnd wrkshp that tw questins needed t be answered t help infrm future investigatins. These questins were answered in TMs 2 and 3 n the fllwing subjects: TM2. TM2 investigated whether slar energy, either fr drying r pwer/heat generatin, culd imprve the verall. 5 new ptins used either slar greenhuses r cncentrating slar arrays cupled with indirect thermal dryers t dry bislids t partially address the evapratin lad n dwnstream thermal prcesses. Optins fr direct prductin f either heat r pwer were als cnsidered. It was determined that the slar cmpnents wuld nt imprve the verall prject ecnmics unless the slar aspects wuld enhance the percentage r amunt f assciated grant funding. TM3. It appeared that cnslidatin f slids handling wuld have many significant benefits; TM3 investigated hw t best cnslidate slids frm three plants at ne site. 6 new ptins were cnsidered and included hauling dewatered WAS; hauling dewatered, digested bislids; WAS frcemains; and WAS frcemains t the service area f the centralized slids handling facilities. It was determined that decmmissining the slids peratins at the NEWRF and NWWRF was indeed beneficial and that WAS frcemains t the SWWRF service area cllectin system wuld save significant peratinal cst. In Wrkshp 3, the results f TMs 2 and 3 were reviewed. It was decided that the slids handling shuld be cnslidated as recmmended in TM3 and that slar ptins culd be cnsidered in the future wuld nt be part f the base prject. It was als decided, based n the existing anaerbic digestin infrastructure at the SWWRF that digestin wuld be included as it helped the verall energy prfile and wuld address the needs created by Flrida Administrative Cde Chapter

4 Anther final shrt list f 10 new/refined ptins was created at Wrkshp 3. These ptins tested varius cnventinal thermal dryers and the pssibility f sale f heat t Eckerd Cllege (lcated immediately adjacent t the SWWRF) in lieu f prducing pwer in excess f that used at the SWWRF. Additinal mass balances and present wrth were develped fr these ptins fr final selectin at the final Wrkshp 4. At Wrkshp 4, a tw-phase apprach was adpted as the recmmended plan. The phases cnsisted f the fllwing elements: 1. Cnslidate all slids prcessing at the SWWRF upgrade the digestin at that plant t Class-A, temperature-phased, anaerbic digestin (TPAD) with 1.2MW f engine-derived pwer. The recmmended elements include: Cnslidating wastewater slids handling by cnveying waste activated sludge (WAS) prduced at the NEWRF and NWWRF t the SWWRF using a cmbinatin f new frcemains and the existing cllectin system. Adding primary clarificatin t the SWWRF t cllect the cnveyed WAS. Upgrading the slids treatment facilities at the SWWRF t Class-A digestin and certificatin f the prduced Class-AA bislids as a fertilizer. Expanding the SWWRF gravity-belt thickening (GBT), digestin, and dewatering capacity t accmmdate the City s entire wastewater slids prductin. Additin f a 1.2- t 1.5-MW digester-gas fueled engine with three-stage gas treatment and bilers fr back-up heat. Prviding a Fat, Oil and Grease (FOG) tipping statin at the SWWRF 2. Yard-waste-fueled thermal prcess (currently envisined as gasificatin with syngas used t fuel internal cmbustin engines). The Phase-2 Prject is n hld as it currently des nt have an imprved present wrth ver the Phase-1 Prject and that the ecnmics and technical feasibility shuld imprve ver time with respect t: Current inability f gasifiers t c-prcess yard waste and bislids. Existing vendrs are cautius and have indicated that separate gasificatin units wuld have t be separately tuned t these different waste streams. In the develped thermal balances, yard-waste derived heat is needed t dry the bislids s that the likely phase-2 gasificatin peratin is fr yard waste nly, with Class-A land applicatin f bislids. This limitatin des nt cnstrain fluid bed cmbustin units. Lack f peratinal US gasifiers that use syngas t fuel internal cmbustin engines. Such cnfiguratins shuld be able t prduce between 50 and 100 percent mre electricity than Rankin-cycle (steam turbine) systems. Prf f this cncept elsewhere is needed (likely either in Germany r Japan) befre implementatin in St. Petersburg. Feasibility t wheel excess pwer t ther City facilities. Implementatin f yard-waste-tenergy will prduce cnsiderably mre pwer than can be used by any ne f the City s existing WRFs. The ecnmic evaluatin assumes that the City can wheel excess pwer t ther City-wned facilities. The feasibility f this ptin has nt yet been verified with Prgress Energy; it has been assumed that excess pwer can be wheeled t ther citywned facilities fr a charge f 0.5 /kwh. Current value f prduced pwer des nt quite satisfy phase-2 ecnmics. In the Feasibility Study, electrical pwer was assumed t be wrth 10 /kwh fr pwer used n site (current prices) and 9.5 /kwh fr electricity used at anther facility. N value has been assumed fr renewable energy credits (RECs). REC value may increase significantly nce the State f Flrida s initial Renewable Prtfli Standard (RPS) cmpliance milestne is reached in 2014, increasing the value f the RECs accrdingly. Higher pwer csts and/r high REC values culd accelerate the phase-2 financial viability.

5 The agreed-upn slutin was defined in TM4. The City Public Wrks Administratr presented the recmmended apprach t the City Cuncil in late July, The presentatin was very psitively received and implementatin effrts are underway. The Feasibility Study methdlgy used is cnsidered very defensible by City staff because: 1. The universe f ptential ptins was cnsidered. These ptins included Class-A and phased anaerbic digestin; gasificatin; fluid-bed incineratin; cnventinal thermal drying; greenhuse and cncentrating slar drying; screw-press, centrifuge, and belt filter press dewatering; generatin f electricity using engines r steam turbines; slids cnslidatin by hauling dewatered WAS r digested slids, sludge frcemain, and sewer cnveyance f WAS; and prductin f/pssible sale f energy in the frm f heat r electrical pwer. 2. City staff participated in the develpment f the ptins and had significant input in the identificatin, develpment, and refinement f the recmmended phases. RECENT UPDATES AND ONGOING DESIGN In early 2013, after cmpletin f the Feasibility Study, the prject renewable fuel directin changed frm renewable electricity prductin t cnversin f digester gas fr use as rcng vehicle fuel in City-wned/Cityperated sanitatin fleet. The vehicle fueling value was mre attractive frm an ecnmic standpint and was even further enhanced by the relatively high value ($1.23/galln diesel equivalent, GDE) f the envirnmental attribute fr renewable vehicle fuels (Renewable Infrmatin Numbers r RINs ) cmpared with RECs. The $1.23/GDE is derived by multiplying a $0.68/galln ethanl equivalent (GEE) publically-traded price by a 1.8GDE/GEE energy factr per equivalent vlumetric fuel value. At this time the pwer csts were adjusted frm an annual average basis f 9.5 t 10 /kwh t match their actual rate structure which cvers different rates fr tw times f day: St. Petersburg pays 16 /kwh fr the 9- hur-per-day peak perid and 6 /kwh fr the 15-hur balance f each day. This distinctin identified that the engines can be very cst effectively run fr 9 hurs per day n natural gas allwing the digester gas t be used predminantly fr vehicle fuel prductin. The scpe f the prject was als increased t include: Cmplete replacement rather than rehabilitatin f tw f the SWWRF s three digesters. This was due principally t the age and cnditin f the existing tanks. Primary clarifier diameter was increased t prvide imprved perfrmance at peak flw cnditins. Gas upgrading system and high-pressure gas cmpressin fr vehicle fuel use. The gas quality after treatment is cmparable t natural gas in terms f heating value and impurities s that this same fuel is usable in the CHP engines as if it were natural gas. The prject is currently in preliminary design and a number f firms are designing the assciated imprvements. Specifically: 3. Brwn and Caldwell is prviding prgrammatic verview and designing the liquid stream integratin, primary clarifiers, digesters and class-a digestin upgrades, digester-gas treatment/vehicle fuel cnversin, and dr cntrl. 4. Black & Veatch is respnsible fr the design f 12kV electrical lp imprvements, engines, and bilers. 5. Crll is designing the GBT thickening upgrades. 6. URS is designing the dewatering and bislids ladut facilities.

6 RESULTS Table 2: 20-year Present Wrth f Current Design Prject Table 2 presents the 2-year, present-wrth csts f the current peratin, cntinued land applicatin f Class-B bislids and the Phase-1 imprvements as currently envisined. Three peratinal mdes are presented in terms f engine peratin n either natural gas r upgraded bigas. The Phase-1 prject: Prduces 1,300 t 1,750 GDE f rcng per day Prduces just under 1 MW f pwer frm a cmbinatin f natural gas and upgraded bigas. Reduces current annual csts f peratin by ~$4.0 t $4.5 millin per year. Has a 20-year present wrth f $35 t $40 millin less than maintaining the status qu. NEXT STEPS The City is currently evaluating the capacity f the SWWRF t handle the additinal lading prpsed under the Phase-1 slids upgrades and the Albert Whitted WRF decmmissining. Discussins are nging t better understand and/r refine the verall directin, specifically: Prgress Energy is being cnsulted n

7 the feasibility and cst implicatins f wheeling pwer frm the SWWRF t ther City-wned electrical demands (like the tw nrthern WRFs). Optins that culd reduce the ttal pwer generated t belw that used at the SWWRF s that wheeling wuld nt be needed: Other ptins fr digester gas use (cleaning and cmpressin t cmpressed natural gas quality fr vehicle fueling r tube-truck cnveyance t ther statinary, gas-fueled engines) are being investigated. Less efficient pwer generatin frm the Phase-2 thermal upgrades s that less capital investment culd reduce the verall life cycle csts. Sale f excess generated pwer t Prgress Energy r thers. Varius cmbinatins f the abve and ther ptins. CONCLUSIONS The prcess emplyed fr the City f St. Petersburg s Bislids- and Yard-Waste-t-Energy Feasibility Study prvided a defensible recmmendatin that met the City s needs. The prcess was effective in large part due t the fluidity f the prcess and willingness t investigate and develp ecnmics analysis fr any and every identified ptin. Cnslidatin f their slids peratin and prducing renewable vehicle fuel and pwer supprt f the City s sustainability and cst reductin gals, and the need t address the State s revised bislids land applicatin rules. The Phase-1 imprvements are planned t be designed by mid-2014 and be peratinal by the end f 2017.