AGL uses Dig­i­tal Twin to op­ti­mise power sta­tion

The Australian Energy Review - - NEWS - CASE STUDY

AGL, for­merly known as the Aus­tralian Gas Light Com­pany, has been in ex­is­tence for over 180 years, be­ing founded in Syd­ney in 1837. As the se­cond com­pany to be listed on the Syd­ney Stock Ex­change, it is not only steeped in his­tory, but is recog­nised as an or­gan­i­sa­tion that read­ily adapts to cus­tomer and mar­ket changes. To­day, AGL En­ergy is in­volved in both the gen­er­a­tion and re­tail­ing of elec­tric­ity and gas for res­i­den­tial and com­mer­cial use. AGL En­ergy’s Tor­rens Is­land Power Sta­tion (TIPS) is lo­cated on Tor­rens Is­land in South Aus­tralia, 18km from Ade­laide’s CBD. The ‘A’ sta­tion be­came op­er­a­tional in 1967, with the ‘B’ sta­tion com­pleted in 1981. The sta­tion burns nat­u­ral gas in boil­ers to gen­er­ate steam, which drives the eight tur­bines to gen­er­ate elec­tric­ity with a to­tal name­plate ca­pac­ity of 1280MW. As the largest power sta­tion in South Aus­tralia, it is a critical as­set, even more so in light of the power gen­er­a­tion chal­lenges en­coun­tered by the state in re­cent years. The team at TIPS have al­ways prided them­selves on the depth of their gen­er­a­tion and op­er­a­tions knowl­edge, keep­ing the sta­tion run­ning at op­ti­mal per­for­mance at all times. In striv­ing to move to the next level, they de­cided to ex­plore the pos­si­bil­ity of im­ple­ment­ing a process sim­u­la­tor, or Dig­i­tal Twin, in 2013. When eval­u­at­ing their re­quire­ments, the team at TIPS took a num­ber of fac­tors into con­sid­er­a­tion. Not only did they want rig­or­ous train­ing for op­er­a­tors in all as­pects of unit, com­mon and lo­cal plant op­er­a­tions, they needed to en­sure that fail­ure and mal­func­tion sit­u­a­tions were ad­dressed quickly and ef­fi­ciently. Such fail­ures and mal­func­tions would need in­ves­ti­gat­ing to iden­tify root causes and pre­vent any repetition. An­other cru­cial as­pect was the test­ing of con­trol and logic mod­i­fi­ca­tions, or pro­posed al­ter­ations to plant op­er­at­ing regime (such as dif­fer­ent burner pat­terns, lower min­i­mum load, higher ramp rates, etc.) with­out hav­ing a detri­men­tal im­pact on op­er­a­tions. Be­ing able to test process and equip­ment mod­i­fi­ca­tion sce­nar­ios us­ing live plant data, yet with­out af­fect­ing op­er­a­tions was a huge at­trac­tion to the TIPS team. With all this in mind, and fol­low­ing a rig­or­ous eval­u­a­tion process, AGL se­lected Yoko­gawa’s Plant+ as the process sim­u­la­tor of choice. Yoko­gawa Aus­tralia & New Zealand has been de­vel­op­ing and im­ple­ment­ing high fi­delity dy­namic sim­u­la­tors for the process in­dus­tries for over 20 years. With a ded­i­cated de­sign and de­vel­op­ment group based in Syd­ney, Yoko­gawa has pro­vided lead­ing edge oper­a­tor train­ing and process op­ti­mi­sa­tion sim­u­la­tors to both do­mes­tic and over­seas mar­kets. These sim­u­la­tors have im­proved op­er­a­tional ef­fi­ciency and safety in the Power Gen­er­a­tion, Oil & Gas and Min­ing sec­tors. With the de­ci­sion made, AGL en­gi­neers moved quickly to im­ple­ment, com­plet­ing in­stal­la­tion of their new Dig­i­tal Twin in 2016. Al­though one of the ini­tial plans was just to train plant op­er­a­tors, they were con­scious of not fall­ing onto the trap many do in just us­ing the sim­u­la­tor as an Oper­a­tor Train­ing Sim­u­la­tor (OTS). Due to time or re­source pres­sures, few process sim­u­la­tor own­ers take ad­van­tage of the full ca­pa­bil­i­ties a Dig­i­tal Twin can pro­vide. The team at TIPS how­ever, had far greater plans, start­ing with in­ves­ti­ga­tions into ef­fects on unit op­er­a­tions when run­ning with­out a Boiler com­bus­tion air pre-heater. Air heaters are an im­por­tant com­po­nent of unit op­er­a­tions from an ef­fi­ciency per­spec­tive. Yet they also re­quire a great deal of main­te­nance to en­sure they are work­ing cor­rectly, with unit ef­fi­ciency sig­nif­i­cantly af­fected when not func­tion­ing cor­rectly. In pe­ri­ods of high de­mand, it is not pos­si­ble to go off­line to re­solve is­sues with air heaters, as the fi­nan­cial im­pli­ca­tions of do­ing so would be sig­nif­i­cant. Yet if an air heater failed dur­ing pe­ri­ods of high de­mand, or an air heater was not func­tion­ing at all, what would be the ef­fect of run­ning a unit with­out the heater? This was a sce­nario that AGL, made a de­ci­sion to test us­ing their Dig­i­tal Twin. There was the very real pos­si­bil­ity that one unit may have to run with­out the airheater dur­ing sum­mer. To as­cer­tain the im­pact on the unit, TIPS con­ducted test­ing on the Sim­u­la­tor to de­ter­mine the ef­fects on the process and also de­fine the lim­i­ta­tions for the Boiler and Tur­bine. “Ob­vi­ously the unit would not achieve full out­put, but we needed to es­tab­lish where the point at which the unit could be run safely and eco­nom­i­cally. We knew we had a chal­lenge on our hands with this air heater and were still go­ing through the process of re­solv­ing it for the long term. How­ever, we had the short-term chal­lenge of en­sur­ing the power sta­tion met con­sumer de­mands and this unit would be cru­cial in do­ing so. We there­fore de­cided to test the ef­fects on a unit of run­ning with­out an air heater to see if this could as­sist in re­solv­ing this short term is­sue.” Us­ing one of the op­er­a­tional units to test this just wasn’t fea­si­ble; sim­i­larly fir­ing up the af­fected unit with­out hav­ing a clear un­der­stand­ing of the im­pli­ca­tions was out of the ques­tion. How­ever, the process sim­u­la­tor is an ideal tool to try out the changes repli­cat­ing op­er­a­tions to a high de­gree. Know­ing that they could run mul­ti­ple sce­nar­ios of unit op­er­a­tions with­out an air heater and mon­i­tor the im­pact on op­er­a­tions was ideal. The team looked at sev­eral ways to run the 200MW unit with­out an air heater, even­tu­ally de­cid­ing to run the unit at 100MW. Then, the idea was to slowly re­move the (model) mass and sur­face area of the air heater un­til only a 2-de­gree heat ex­change tran­spired, which was seen as be­ing the best out­come. Later re­mov­ing this re­stric­tion, AGL could sim­u­late less back­pres­sure on the Forced Draft fans. “The test­ing was com­pleted in a lim­ited time­frame but the re­sults seemed to re­flect what we ex­pected. As the fans worked harder, fuel gas pres­sure was higher and at about 160MW the air and fuel be­came un­sta­ble so would re­quire some tun­ing.” Next, the unit was taken through all loads up to 160MW with a re­duced ramp rate with­out any is­sues. With­out re­stric­tion, sev­eral boiler purges were then per­formed suc­cess­fully and once more the ex­pected re­sults were ob­served, with lower wind­box pres­sures for given fan po­si­tions. “Test­ing in­cluded clos­ing in the stack damper slightly to see if it was an op­tion to in­crease pres­sure to nor­mal and this worked too. We also didn’t need to force any of the safety sys­tem pa­ram­e­ters and the trip set­tings were not breached.” Us­ing their Dig­i­tal Twin, TIPS con­firmed their be­lief that run­ning with­out an air heater would be pos­si­ble. Not an ideal sce­nario, but know­ing they can op­er­ate the af­fected unit to meet con­sumer de­mand in the short term and even op­er­ate other units with­out air heaters for short pe­ri­ods pro­vides op­tions. In the pres­surised and high pro­file en­vi­ron­ment of power gen­er­a­tion in South Aus­tralia, AGL‘S adop­tion of a Dig­i­tal Twin has pro­vided clear ev­i­dence that process per­for­mance can be op­ti­mised in re­sponse to plant con­straints.

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