L aboratory of P hysical and A nalytical C hemistry KULeuven Department of Chemistry Laboratory for Physical and Analytical Chemistry (LPAC) Celestijnenlaan 200 F 3001 Leuven Belgium Tel: Fax: Technical Meeting, Offenburg, 22/09/2005

WP 1.4. : O 3 generation testbed (constructed by Copperline and Seaking) L aboratory of P hysical and A nalytical C hemistry Ozone generation testbed:  Installed at LPAC-laboratory on 6 and 7 july 2005 Prof. Thomas Rose (FH Münster; Reward-coördinator) Klaus Padtberg (Hobart) Reiner Preuss(Copperline) Arthur Gregor(Copperline) Prof. Chris Vinckier(K.U.Leuven, LPAC) Frank De Smedt(K.U.Leuven, LPAC) Hans Vankerckhoven(K.U.Leuven, LPAC)  First tests on the installation days  Afterwards further testing by LPAC

WP 1.4. : O 3 generation testbed L aboratory of P hysical and A nalytical C hemistry O 3 generator box nr 1 Storage tank Water jet (Venturi-system) FRONT VIEW External control of O 3 boxes by means of ETR-CL software MAXO Box nr 2 Water pump (stainless steel)

O 3 generation testbed: 2 modules L aboratory of P hysical and A nalytical C hemistry MODULE 1: Two ozone generation boxes, designed by Copperline and constructed by CL and Seaking Air inlet and introduction into the Venturi injector MODULE 2: Venturi injector (mixing of gas and water) Water pump (external water loop) Storage tank (designed and constructed by Copperline and Seaking)

O 3 generation testbed L aboratory of P hysical and A nalytical C hemistry MODULE 1

O 3 generation testbed (Module 1) L aboratory of P hysical and A nalytical C hemistry Two ozone boxes Gardena Tubing connecting Box 1 and 2

O 3 generation testbed (Module 1) L aboratory of P hysical and A nalytical C hemistry

O 3 generation testbed (Module 1): preliminary experiments (july 2005) L aboratory of P hysical and A nalytical C hemistry Maximum gas phase concentration achieved with the CL ozone boxes = 2 g/m 3 O 3 ≈ 0.1 v/v % O 3 (target: 0.5 – 1.0 % v/v) Ozone boxes : pressure drop between inlet and introduction into Venturi: leaks ! (Gardena Tubing ? Sealing of the boxes ?...) Ozone in the water: maximum = 20 µg/l O 3 (20 ppb): target ≈ 1 mg/l O 3 for disinfection (dose = time x concentration). Modifications to design of the boxes Note: technology should work, cfr. O 3 Congress Strasbourg august 2005

O 3 generation testbed L aboratory of P hysical and A nalytical C hemistry MODULE 2

O 3 generation testbed (Module 2): construction scheme L aboratory of P hysical and A nalytical C hemistry

O 3 generation testbed: experiments L aboratory of P hysical and A nalytical C hemistry Storage tank Water jet (Venturi-system) Water pump (stainless steel) Start of the external water loop

O 3 generation testbed: experiments L aboratory of P hysical and A nalytical C hemistry

O 3 generation testbed: experiments L aboratory of P hysical and A nalytical C hemistry Venturi injector

O 3 generation testbed: experiments L aboratory of P hysical and A nalytical C hemistry Upper part water loop

O 3 generation testbed: experiments L aboratory of P hysical and A nalytical C hemistry Gas phase  Phase separation (no mixing)

O 3 generation testbed: experiments L aboratory of P hysical and A nalytical C hemistry Introduction in storage tank

O 3 generation testbed: experiments L aboratory of P hysical and A nalytical C hemistry

O 3 generation testbed: experiments L aboratory of P hysical and A nalytical C hemistry Characterisation of the air (Q air ) & water (Q water ) flows Determination of the mass transfer coefficient k L a Monitoring of pH, temperature, ORP and conductivity Conclusions Further implementations, improvements,.... OUTLINE

O 3 generation testbed: experiments L aboratory of P hysical and A nalytical C hemistry Characterisation of the air (Q air ) & water (Q water ) flows Q water Q air Regulators: No real fine-tuning

O 3 generation testbed: experiments L aboratory of P hysical and A nalytical C hemistry Characterisation of the air (Q air ) & water (Q water ) flows Q air depends on Q water and on the number of turns of the air regulator Reproducibility only within 10 % (regulators)

O 3 generation testbed: experiments L aboratory of P hysical and A nalytical C hemistry Determination of the mass transfer coefficient k L a  Ozone from the LPAC-setup Experimental procedure

O 3 generation testbed: experiments L aboratory of P hysical and A nalytical C hemistry Determination of the mass transfer coefficient k L a The ozone concentration in the water of the storage tank as a function of time (the first 5 hours were used for equilibrating the system and are not displayed) at (38.8 ± 0.5)°C, Q O2/O3 = 60 dm 3 /hour and pH (5.60 ± 0.1). A) and B) Q water = 3.1 l/min and [O 3 ] gas = 22.6, respectively 25.4 g/m 3, C) Qwater = 2.0 l/min and [O 3 ] gas = 28.3 g/m 3 (more details: Table 1).

O 3 generation testbed: experiments L aboratory of P hysical and A nalytical C hemistry Determination of the mass transfer coefficient k L a

O 3 generation testbed: experiments L aboratory of P hysical and A nalytical C hemistry Determination of the mass transfer coefficient k L a  k L a depending on Q O2/O3 at low Q water, no dependence at higher Q water  k L a depending on Q water  k L a = 13 hour -1 (60 dm 3 /hour gas flow): literature values 10 x higher for Venturi ! (mixing problems ?)  t sat,90 = 12 min (Q water = 3.1 l/min) and 20 min (2.0 l/min)  t degas = 25 minutes

O 3 generation testbed: experiments L aboratory of P hysical and A nalytical C hemistry temperature and ORP Fast increase at ozone buildup Slow decrease at O 3 degassing  Feasibility as monitor for O 3 concentration ? (perhaps qualitative) Temperature increase (initially) till 36 – 39°C (pump ?)

O 3 generation testbed: experiments L aboratory of P hysical and A nalytical C hemistry pH and conductivity pH follows the on-off cycle of the O 3 generator (introduction of organic species and/or NO x ?) Conductivity increase a.f.o. time : more increase when O 3 is produced (cumulative).

O 3 generation testbed: experiments L aboratory of P hysical and A nalytical C hemistry Summary of the results Q air depends on the air flow regulator and Q water due to the non-accurate regulators & meters, reproducibility is only within 10% the gas flow initially requires 3 to 4 hours to stabilize the temperature of the storage tank water stabilizes at about 39°C after 3 to 4 hours (due to the water pump heating) the mass transfer coefficient k L a, a measure for transfer rate of ozone from gas to liquid phase, is determined for the Venturi system installed and found to be dependent on Q water, i.e. an increase of about 30% is observed when Q water is changed from 2 to 3.1 l/min k L a is about 13 hour -1 when Q water =3.1 l/min and Q O2/O3 = 60 dm 3 /hour the external water loop contains a tubing part where the gas and liquid phase are separated, so no mixing occurs in this zone (especially between Venturi and tank) t sat,90 equals approximately 12 minutes at Q water = 3.1 l/min and 20 minutes at Q water = 2.0 l/min

O 3 generation testbed: experiments L aboratory of P hysical and A nalytical C hemistry Summary of the results the time needed to degas (de-ozonize) the water completely is 25 minutes when the ozone concentration in the water increases, the ORP-signal sharply increases. When the storage tank water is de-ozonized the ORP-signal drops more slowly than does the ozone concentration in the water. An increase of the conductivity is observed during recirculation and during ozonation. In the latter case the increase of the conductivity is much more pronounced, probably caused by the introduction of organic species or NO x into the water. The effect on conductivity of the various on-off cycles is cumulative. The pH evolution during ozonation and degassing needs to be further investigated and perhaps related to the conductivity changes. The pH follows the on-off cycles of the ozone generator. At Q water = 3.1 l/min and Q O2/O3 = 60 dm 3 /hour the ozone concentration in the liquid equals 8.4 mg/l for 22.6 g/m 3 O 3 (± 1.0 % v/v O 3 ) at pH 5.6 and 39°C. Pressure and/or temperature effects due to the Venturi system are possibly influencing the ozone concentration in the liquid, namely increasing the ozone solubility. These effects will be investigated more thoroughly.

O 3 generation testbed: experiments L aboratory of P hysical and A nalytical C hemistry General conclusions  Design needs to be improved ! (e.g. phase separation in the upper part of the tubing, inlet of gas/water in the storage tank, …) Venturi systems in literature 10 x times higher k L a values than currently reached (higher gas flows ?)  ORP not feasible as ozone monitor (quantitative: NO ; qualitative: perhaps)  Ozone liquid steady state concentration Apparently an enhanced solubility (more experiments)

O 3 generation testbed: experiments L aboratory of P hysical and A nalytical C hemistry future  Design adjustments  Ozone steady state concentration: more research  Higher gas flows: k L a determination  Ozone generation modules after adaptions by CL and Seaking: evaluation of [O 3 ] gas a.f.o. ……… Note: cfr Report 1: at high pH and temperature: difficult to achieve ozone concentrations in the water (k L a and [O 3 ] gas ).