Case Study: A Coatings Plant Replaced Manual Lance Washing With an Automated Tank Cleaning Machine

Pigment left on a vessel wall costs a whole batch. A coating mixed in a dirty tank can fail on colour, on gloss or on adhesion after it has filled a tote. That risk landed on the batch after every colour change at a mid-size coatings plant in Europe.

The plant runs 12 mixing vessels from 3,000 to 15,000 L on solvent-borne acrylic and alkyd. Changeover was manual, with a worker inside on a solvent lance and a static spray ball rinse from the top. The job ran 45 to 70 minutes, and a VOC exposure permit bound the method.

Case Snapshot

The figures below are the generic shape of this class of installation, not a plant record.

Item	Value
Industry	Industrial coatings and synthetic resin, paint industry duty
Region	Mid-size plant in Europe, anonymised
Vessels	12 chemical mixing tanks, 3,000 to 15,000 L
Chemistry	Solvent-borne acrylic and alkyd, pigment changeover
Before	Manual solvent lance plus one static spray ball per vessel
After	Retractable rotary jet on a manway carriage, six of twelve vessels
CIP skid	Two-stage rinse, solvent recovery loop, validated rinse check
Changeover time	45 to 70 minutes before, 38 minutes after
Fresh solvent per changeover	About 18 L before, about 4 L after
Aqueous liquor per changeover	About 500 L before, about 880 L after
Residue result	Streak failures after a colour change before, clean swabs after

• Design point: 110 L/min at 4 bar at the head.
• Coverage radius: 1,200 to 2,400 mm from the vessel axis.
• Cycle: 8 minutes aqueous plus 4 minutes solvent, 12 minutes total.
• Solvent budget: 18 L of fresh solvent down to 4 L per changeover.

A 15,000 L chemical mixing tank of this class carries about 35 m² of wetted surface, heads included. A 12,000 L vessel carries about 30 m², which sets the coverage arithmetic below.

The Challenge

The plant changed colour or grade three times a day on its busiest vessels. Two of the twelve ran near-continuous pigment work. The rest changed over two to five times a week, and all twelve were cleaned by hand from the inside.

A worker opened the manway and entered with a solvent lance fed from a reclaim drum. The lance passed about 20 L/min for 25 minutes, so about 500 L crossed the wall. The operator then wiped the pigment bands with neat solvent, drawing about 18 L of fresh solvent per changeover. A static spray ball finished with a rinse at 130 to 200 L/min and 1.5 to 2 bar.

Three costs came out of that method. The direct cost was solvent. Six vessels at three changeovers a day over 250 days drew 18 L of fresh solvent each time. That is 81,000 L a year through the cleaning step alone.

The second cost was production time. A 45 to 70 minute changeover on a 12,000 L vessel is a reactor that could be making product.

The third cost could not be scheduled. Pigment that survived the wash on the upper shell could release into the batch after a colour change. A streak there is a rejection after the raw materials, the grinding time and the quality work are spent. One rejection a quarter funded the project.

The VOC permit set the outer boundary. A worker inside a vessel on an open lance draws vapour in the breathing zone. The permit therefore carried exposure monitoring and an entry procedure.

Why a Static Spray Ball Fails on Solvent-Borne Resin

A static spray ball is a wetting device. Published duty for the class runs 130 to 200 L/min at 1.5 to 2 bar, and that flow spreads over a full sphere. Liquid reaches the wall as a thin sheet with little momentum behind it.

Published wetting targets for cleaning coverage run about 0.4 to 0.6 L/min per square metre. On a 12,000 L vessel with about 30 m² of wetted area, a 20 L/min lance pass delivers 0.67 L/min per m². The lance already sat above the published wetting floor. The vessel still failed.

Two mechanisms explain the gap.

The film is not water soluble. Acrylic and alkyd resin on a warm wall cross links as solvent flashes off. Detergent softens the outer skin and leaves the anchor layer on the steel.

The wall is crowded. A chemical mixing tank carries an agitator shaft, baffles, a dip tube, a probe and a sample line. Each item casts a dry shadow. The ball keeps that shadow wet without stripping it, and a pigment band of 0.2 mm then reads as clean under a torch.

What an Automated Tank Cleaning Machine Changes

An automated tank cleaning machine replaces the flooded sphere with a swept jet. The device here is a fluid-driven rotary jet on a retractable carriage. It enters through the manway, extends on a tubular lance, washes, and retracts flush with the cover so the batch can be charged.

Three things change together.

The jet becomes coherent and repeating. Two or three nozzles pass the whole 110 L/min through orifices near 6 mm. The head turns that flow into hard jets that sweep a fixed pattern. Every point therefore takes many impacts inside one rotation. The rotary jet head guide sets out the pattern logic for this class.

The path becomes defined. The carriage centres the head on the vessel axis, so the distance to the wall is equal in all directions. A pattern that repeats exactly is one a plant can log, and a logged cycle is what a cleaning validation rests on.

The vessel stays closed. The cover carries the carriage, so the tank washing machine runs sealed with the extraction duct connected. The agitator seal flush stays live through the cycle, which keeps the seal faces clear of wash liquor and pigment fines.

The Solution

The retrofit covered six of the twelve vessels. A retractable rotary jet went onto the manway of each one, fed by the existing CIP skid. The remaining six kept their static spray balls, because their duty is single product. The six converted vessels now run as one automatic tank cleaning system, and each automated tank cleaning machine on the manifold takes the same feed.

Vessel	Duty	Machine type	Coverage radius	Flow	Pressure
V-01, 15,000 L vertical	Alkyd resin let-down	Retractable rotary jet, three-jet head	2,400 mm	110 L/min	4 bar
V-02, 12,000 L vertical	Acrylic pigment dispersion	Retractable rotary jet, three-jet head	2,200 mm	110 L/min	4 bar
V-03, 12,000 L horizontal	Clear coat let-down	Retractable rotary jet, three-jet head	2,400 mm	110 L/min	4 bar
V-04, 8,000 L vertical	Acrylic grind paste	Retractable rotary jet, two-jet head	1,800 mm	95 L/min	4 bar
V-05, 5,000 L vertical	Small alkyd batch	Retractable rotary jet, two-jet head	1,500 mm	85 L/min	3.5 bar
V-06, 3,000 L horizontal	Thinner and let-down	Retractable rotary jet, two-jet head	1,200 mm	80 L/min	3 bar
V-07 to V-12	Mixed single-product duty	Static spray ball retained, lance for spot work	600 to 1,200 mm	130 to 200 L/min	2 bar

Every machine point sits inside the published envelope. The class band for a 1.5 inch (38 mm) device is about 95 to 120 L/min at 3 bar. The design point of 110 L/min at 4 bar converts back to 95 L/min at 3 bar. The skid pump holds that flow with a loaded filter.

The retained spray balls stay in their own band of 130 to 200 L/min at 1.5 to 2 bar. They still pre-rinse and flush.

Cleaning Chemistry and Cycle Budget

The two-stage rinse is the core of the change. A single water wash cannot remove a cross-linked resin film, and a single solvent wash leaves pigment in the sludge that returns to the wall.

Stage one is aqueous. Water at 45 to 55 °C with an alkaline detergent lifts loose pigment and filler. The automated tank cleaning machine runs this stage for 8 minutes at 110 L/min, so about 880 L passes through the vessel. The plant dumps and remakes this charge at each changeover. That is why the aqueous volume rises. A shared charge would carry pigment from a dark batch into a light one.

Stage two is the solvent stage. The tank washing machine draws a xylene-class solvent from the recovery loop at 110 L/min for 4 minutes, so about 440 L crosses the wall. The loop filters out pigment, separates water and returns the solvent. Fresh make-up falls to about 4 L per changeover.

The solvent recovery loop is what makes the cycle affordable. The manual reclaim drum built up pigment and water over a shift. The liquor returning to the wall was therefore dirtier than the liquor the plant bought. Filtration and distillation return a clean fraction.

Wash time is 12 minutes, and the full changeover time is 38 minutes. Drain, dry, extension, retraction and the release check fill the rest of that window. The CIP tank washing systems guide covers the same loop architecture at this scale.

The Arithmetic

Four calculations carry this case. Every input is labelled as class data, a plant figure or a working estimate.

Rotary jet flow against pressure. Flow through a fixed orifice rises with the square root of pressure, so GPM2 = GPM1 x sqrt(P2 / P1). A 1.5 inch (38 mm) rotary jet device of this class passes about 95 to 120 L/min at 3 bar. That is a published band for the class. Take the low end at 95 L/min and raise pressure from 3 bar to 5 bar. The result is 95 x sqrt(5 / 3) = 95 x 1.291 = 123 L/min. The design point scales the same way, giving 110 x sqrt(5 / 4) = 110 x 1.118 = 123 L/min. Both routes agree, which is a useful cross check on the pump curve.

The orifice basis. For water-like fluid, Q (L/min) = 0.65 x d (mm)² x sqrt(P (bar)), with a discharge coefficient near 0.95. Solve for the equivalent orifice at the design point. Then d² = 110 / (0.65 x sqrt(4)) = 110 / 1.30 = 84.6 mm², so d = 9.2 mm. A three-jet head splits that into three orifices of 84.6 / 3 = 28.2 mm² each, which is 6.0 mm across.

The solvent correction. A 25 °C xylene-like solvent has a relative viscosity of about 0.91 against water. A correction of 1 / sqrt(0.91) = 1.048 lifts the same orifice about 5 percent, so 123 L/min at 5 bar becomes about 129 L/min. Treat that as a working estimate. The discharge coefficient barely moves with viscosity at these Reynolds numbers, so the flow gain is small and the momentum gain is smaller.

The volume ledger. Liquor per changeover is flow times minutes. The manual method passed 20 L/min for 25 minutes, which is 500 L, plus 18 L of fresh solvent in the wipe passes. The machine passes 110 L/min for 12 minutes, which is 1,320 L, split into 880 L aqueous and 440 L solvent.

Step	Manual lance and static ball	Automated tank cleaning machine
Aqueous liquor	500 L, 20 L/min for 25 min	880 L, 110 L/min for 8 min
Solvent liquor	18 L of fresh solvent, hand wipe	440 L recirculated, 110 L/min for 4 min
Fresh solvent make-up	18 L per changeover	4 L per changeover
Total liquor through the vessel	518 L	1,320 L

Total liquid goes up, not down. Aqueous volume rises 380 L per changeover while fresh solvent falls 14 L. The economics do not sit on water. They sit on solvent price and VOC fees.

Per year. Six vessels at three changeovers a day over 250 production days gives 6 x 3 x 250 = 4,500 changeovers a year. Solvent falls by 4,500 x 14 = 63,000 L a year. Aqueous liquor rises by 4,500 x 380 = 1,710,000 L, or 1,710 m³, a year. Water supply and effluent are assumed at EUR 1.20 and EUR 1.80 per m³. Extra water and disposal then costs 1,710 x 3.00 = EUR 5,130 a year.

The payback band. Three inputs are assumptions, not quotations. Solvent price is EUR 2.20 per L. The VOC permit charge is EUR 1.80 per kg on the solvent fraction leaving the process. Loop running cost, covering pump energy, filters, distillation and sludge disposal, is EUR 20,000 to EUR 45,000 a year.

Solvent purchase avoided is 63,000 x 2.20 = EUR 138,600 a year. Xylene-class solvent at 0.86 kg/L means 18 x 0.86 = 15.5 kg charged per manual changeover. At an assumed 70 percent fugitive fraction about 10.8 kg escapes. The sealed machine vents an estimated 0.9 kg, so the reduction is 10.8 - 0.9 = 9.9 kg. That is 4,500 x 9.9 = 44,550 kg a year, and a fee credit of 44,550 x 1.80 = EUR 80,190.

Gross credit is 138,600 + 80,190 = EUR 218,790 a year. Subtract the EUR 5,130 water and disposal debit and the loop running cost. Net saving lands between about EUR 169,000 and EUR 194,000 a year. If only colour and grade changes need the full two-stage cycle, that is 60 percent of the changeovers. The credits then scale to about EUR 101,000 to EUR 116,000 a year.

Capital for six machines with carriages plus the skid rework is an assumed EUR 190,000 to EUR 350,000. The fast end of the payback band is 190,000 / 116,000 = 1.6 years. The slow end is 350,000 / 101,000 = 3.5 years. A band is the honest form of the answer. A single payback figure for an unsurveyed plant would be a guess with a decimal point. The nozzle flow rate calculation guide carries the orifice equation used above.

Coverage and Impact Pressure Math

Coverage geometry decides whether a machine reaches the whole vessel. Impact decides whether it cleans what it reaches.

Published throw for a 25 degree full cone jet at 3 bar runs roughly 4 to 6 m for this class. The 15,000 L vessel has a 2,400 mm inside diameter. The device sits on the top manway, centred on the axis. The bottom head is 2,400 mm below the nozzle, and a dished head adds about 0.15 x 2,400 = 360 mm. The worst case distance is about 2,760 mm.

That leaves real margin. At the low end of the band, 4.0 / 2.76 = 1.45 times the worst case. At the high end, 6.0 / 2.76 = 2.17 times. The device is not sizing against the edge of its throw curve.

Impact falls as the jet travels, at roughly the reciprocal of distance in published practice. A point at 2.76 m takes about 1.8 times the impact of a point at 5 m. Buying reach with pressure is expensive, so this design shortens the path instead.

Centring earns its place with a simple ratio. On the axis, every wall point is 1,200 mm from the nozzle, so impact is uniform. Move the carriage 400 mm off axis and the near wall is 800 mm away while the far wall is 1,600 mm away. Impact halves on the far side, which is where a pigment band survives.

Pattern width follows width = 2 x d x tan(theta / 2). For a 25 degree jet the half angle is 12.5 degrees and tan(12.5) = 0.2217, so width = 0.443 x d. The strip is 0.532 m wide at the 1,200 mm shell radius and 1.224 m wide at the 2,760 mm bottom knuckle.

The strip count sets the sweep. The shell circumference at that radius is 2 x pi x 1.2 = 7.54 m. With 12.5 percent overlap the pitch is 0.466 m, so the sweep needs 16.2 strips. A two-axis rotary jet then walks its tilt from the top tangent to the bottom knuckle. The spray angle guide covers the same geometry for fan and cone families.

Engineering Validation and Swab Criteria

The plant does not release a vessel on a visual check. It releases on a logged cycle plus evidence that the cycle worked.

Coverage is proved with a fluorescent dye test before the cycle is fixed. The vessel is sprayed, washed, then inspected under ultraviolet light. Dim areas map the shadow zones, and the dye test moved the machine position on two horizontal vessels.

The cleaning validation then runs in three layers.

The swab test leads. Worst-case points are swabbed after each cycle, starting with the manway cover underside and the far shell quadrant. The agitator shaft above the impeller, one baffle edge, the bottom knuckle and the discharge valve seat follow. Those points carry the longest travel or the worst shadow. A swab test on a clean surface shows no visible residue and a reading under the plant limit.

The rinse check follows. A sample of the aqueous stage drain is analysed for total organic carbon. Total organic carbon measures the organic loading left on the last wetted surface. It catches resin residue that a swab can miss on a welded seam. The working limit here is a total organic carbon reading no more than 2 mg/L above the incoming water baseline. That is a plant figure set at validation, not a published standard.

The record closes the loop. Each cycle logs flow, pressure, time and rotation for both stages, and a cycle below the flow setpoint is flagged rather than accepted. A fluid-driven head that loses flow turns slowly and lays a partial pattern while the timer keeps counting.

Wetted parts are 316L stainless, and the carriage seals are rated for xylene-class solvent. The tank cleaning nozzle selection guide covers the same selection path for vessel geometry and residue class.

The Results

The table below is a range picture for this class of retrofit, not a plant audit record.

Metric	Manual lance and static ball	Automated tank cleaning machine	Basis
Changeover time	45 to 70 min	38 min	Logged cycle time
Wash phase	About 25 min of lance work	12 min, 8 aqueous plus 4 solvent	Plant cycle sheet
Fresh solvent per changeover	About 18 L	About 4 L on the recovery loop	Drum issue against top-up log
Aqueous liquor per changeover	500 L	880 L	Metered flow at the head
Manual entry	Worker inside with a lance	Vessel closed and sealed	Permit condition
Agitator seal	Flush throttled during entry	agitator seal flush live through the cycle	Standard practice on this duty
Residue after a colour change	Streak rejections on some changeovers	Clean swab and total organic carbon result	Swab and rinse records
Water and effluent	500 L per changeover	880 L, 1,710 m³ a year more	Metered

The changeover time is the number the plant feels every shift. The manual window ran 45 to 70 minutes against 38 minutes on the logged cycle, which returns 7 to 32 minutes per vessel turn.

That is what an automatic tank cleaning system buys a coatings plant on pigment duty. It buys repeatability, because the tank returns to a defined clean state that the plant can prove.

Reading the Numbers Against Published Ranges

Every figure here sits inside a band, or is labelled as a plant figure or a working estimate.

The chosen device sits at the low end of its class. Published duty for a 1.5 inch rotary jet device runs about 95 to 120 L/min at 3 bar. The design point of 110 L/min at 4 bar converts to 95 L/min at 3 bar by the square root rule. An automated tank cleaning machine at the bottom of the published band is a deliberate choice here. A smaller device wears more slowly.

Throw sits inside the band with margin. Published throw for a 25 degree full cone jet at 3 bar runs roughly 4 to 6 m for this class. The worst case distance is about 2.76 m, leaving 1.45 to 2.17 times of margin.

Caveats protect the case. The aqueous volume only rises because this plant dumps its stage one charge at each changeover. A plant that recirculates that charge sees a much smaller water increase. The payback band also assumes the VOC charge applies to the full solvent stream, so read the permit before the model.

The flow and throw rules are the transferable part. Any vessel in this class on solvent-borne resin can be sized from the wetted area, the worst case throw distance and the solvent stage volume.

Why This Matters

The transferable asset is a method, not a device list. Coverage, impact, chemistry and proof are the four variables, and they interact. A jet that reaches every wall point still fails if the solvent returns pigment to the surface. A clean vessel still fails an audit if the cycle cannot be logged.

The paint industry meets this pattern on a schedule. Pigment changes are frequent, batches are valuable, and the solvent carries both a purchase price and a permit cost. Here the honest water number rises while the solvent number falls. That trade is right whenever solvent costs many times what water and effluent cost together.

An automated tank cleaning machine also took a person out of the vapour zone, which never shows in a payback model. A sealed vessel with a live agitator seal flush is a different permit conversation. The worker is no longer inside a chemical mixing tank with an open lance.

The Next Step

BoreJet supplies the nozzles and does the sizing behind them. That covers flow at pressure, pattern geometry, the recovery loop and drain detail for this class.

Send the vessel drawing, the wetted area, the residue class and the cleaning chemistry through the contact page. The response comes back with the machine count, the orifice sizes and the cycle that fits the changeover window. The hardware sits in the tank cleaning products range. The solvent and mist side of the same loop is covered in the air atomizing nozzles range.