H₂ Ready!

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Initial situation

Most coun­tries in the world want to decar­bonize their indus­try in the next 20 years. In impor­tant sec­tors such as steel and met­al pro­duc­tion and the chem­i­cal indus­try, as well as in large-scale trans­port by ship, plane and truck, this will only be pos­si­ble with large quan­ti­ties of hydro­gen (H₂). How­ev­er, hydro­gen is only emis­sion-free if the elec­tric­i­ty for elec­trol­y­sis and fur­ther pro­cess­ing comes from renew­able ener­gy sources—in which case we can speak of “green hydro­gen.”

But CO₂-free hydro­gen pro­duc­tion will only become more wide­ly usable if pro­duc­tion costs are low­ered. To this end, immense invest­ments are being made in the pro­duc­tion of green hydro­gen by gov­ern­ments as well as pri­vate funds and investors. And here is where MR comes in. Hel­ton Hen­rique Bez­er­ra, MR’s expert for elec­trol­y­sis, explains: “We advise oper­a­tors and investors from the plan­ning phase to the com­mis­sion­ing of the plant. If we are involved in the process at an ear­ly stage, invest­ment costs can be sig­nif­i­cant­ly reduced and the prof­itabil­i­ty as well as the ser­vice life of the plants can be increased.” One way in which this is done is by solv­ing the input-volt­age prob­lem at the elec­trolyz­er.

The problem with electrolyzer operation

Elec­trolyz­ers that are fed with fluc­tu­at­ing ener­gy from wind or pho­to­voltaics have to adjust their pro­duc­tion depend­ing on how much elec­tric­i­ty is avail­able for them at any giv­en time. Since almost all H₂ plants work with direct cur­rent, the fluc­tu­a­tions in hydro­gen pro­duc­tion as well as age­ing of the elec­trolyt­ic cells caus­es exces­sive rec­ti­fi­er oper­a­tion. With spe­cial­ized con­cepts from MR, rec­ti­fi­er oper­a­tion can be opti­mized by con­trol­ling the input volt­age.

Satya­jit Pandya, who works in pow­er qual­i­ty at MR, knows the prob­lems this caus­es: “Elec­trolyz­er oper­a­tion with­out appro­pri­ate input volt­age con­trol would lead to high­er har­mon­ic and reac­tive pow­er require­ments,” both of which must be com­pen­sat­ed by cost­ly fil­ters and expen­sive com­pen­sa­tion devices. In addi­tion, poor­ly con­trolled input volt­ages dam­age the sen­si­tive cells in the elec­trolyz­er and reduce its per­for­mance over its life cycle (so-called “volt­age drop”) lead­ing to a short­er life of the plant over­all.

The vacuum on-load tap-changer as a solution

In this regard, MR offers a com­bi­na­tion of vac­u­um on-load tap-chang­er and thyris­tor rec­ti­fi­er that has proven itself on the mar­ket for decades. “Over the past 30 years, we have super­vised more than 40 hydro­gen projects, so we know exact­ly what is impor­tant in these plants,” Pandya empha­sizes. The vac­u­um on-load tap-chang­er opti­mizes the steady-state volt­age adjust­ment which, in turn, reduces the elec­tri­cal inter­fer­ence loads and har­mon­ics in the sys­tem by about 40 per­cent.

This accord­ing­ly low­ers the need for com­pen­sa­tion by pow­er qual­i­ty man­age­ment sys­tems such as har­mon­ic fil­ters, there­by reduc­ing invest­ment vol­umes and oper­at­ing costs. The same applies to reac­tive-pow­er com­pen­sa­tion for which the vac­u­um on-load tap-chang­er also achieves a reduc­tion of 40 per­cent. Fur­ther­more, adds Bez­er­ra, “Our VACUTAP® on-load tap-chang­ers are main­te­nance-free up to 300,000 switch­ing oper­a­tions”.

And because this solu­tion requires less hard­ware over­all, the space required around the H2 plant is also reduced. Fur­ther­more, the sen­si­tive cells in the elec­trolyz­er expe­ri­ence less stress due to the opti­mized volt­age con­trol allow­ing the pow­er fac­tor of the plant to remain high over a long peri­od of time with a soft­er and slow­er volt­age drop. Bez­er­ra points out anoth­er advan­tage: “The over­all ser­vice life of the H2 plant is increased by years, which con­sid­er­ably increas­es the prof­itabil­i­ty of the invest­ment!”