Condenser Rubber Ball Cleaning Systems: Ball Size, Quantity and Dosing Rate

Abstract: A rubber ball system does not fail because it was never installed; it fails on three figures - ball diameter, ball quantity and dosing rate. One millimetre out on diameter, or a dosing rate down at 70%, and the end difference climbs back to 8 C. This article works through the components, the sizing figures and the operating discipline: wet ball diameter 1-2 mm above the tube bore, ball quantity at 10-15% of the tubes in one pass, dosing rate not below 95% and recovery not below 90%, with troubleshooting run in the order ball diameter, ball quantity, collection screen, pump and valves. The sequence against shutdown chemical cleaning and water jetting cannot be reversed. Figures follow DL/T 957-2017 and GB/T 25146-2010, and an anonymised retrofit on a 300 MW unit closes the article.

1. Position First: Rubber Ball Cleaning Maintains, It Does Not Descale

Rubber ball cleaning stops scale from settling in; it does not remove scale that has already settled. The ball bears on the tube wall because its wet diameter is slightly larger than the bore, and the circulating water carries it through the bundle tube by tube, wiping off soft deposits, slime and biofilm while they are still fresh. Once a carbonate layer above 0.3 mm has formed, the ball bounces off the tube inlet: it cannot cut the hard layer, and the contact wears the ball faster at the same time.

Two figures decide whether a condenser can be held on balls alone. The first is deposit type: open the water box and sample it, and a carbonate or silicate layer identified by acid solubility is beyond what a ball can handle. The second is the cleanliness factor: between 0.80 and 0.90 the bundle is in reasonable order and the ball system can hold it there; below 0.70, with the end difference past 8 C, the unit needs a shutdown chemical clean or tube-by-tube water jetting first, and only then goes back to ball maintenance.

Getting the order wrong costs directly. On a scaled condenser at one plant we saw a month of continuous dosing: recovery slid from 92% to 74%, more than 40 balls a day had to be topped up, the end difference moved by only 0.3 C, and the job ended in a chemical clean with a fresh charge of balls on top.

2. System Components: the Collection Screen and the Ball Counter Are the Ones Left Out

A complete system is a charging chamber, a ball pump, a distributor, a collection screen and a counter, and the dosing rate suffers wherever one of them is cut back. The chamber holds and measures the charge and needs a sight glass and a drain valve; the pump carries the balls into the water box with the circulating water; the distributor decides how evenly they are split between passes and tube zones; the collection screen catches them on the outlet side; the counter records the number thrown in and the number returned, which is where the management data comes from.

The collection screen is the component most often in trouble. Mesh size follows from the ball diameter and is normally set at 60-70% of the wet ball diameter, small enough to keep the worn balls and open enough not to lift the differential across the screen; flow area is sized at 1.5-2 times the circulating water flow, and the differential is watched in service, since a rising differential means debris on the mesh or balls stacking up in front of it. The secondary strainer and the collection screen are two different items - the strainer keeps debris out of the circulating water, the screen recovers balls - and sites that confuse them are usually the ones with a recovery problem.

The pump and the distributor have to be read together. Pump flow is set from the circulating water flow per pass so that the velocity inside the tubes stays at 1.5 m/s or above, and the distributor outlet is aligned with the tubesheet, because a biased distributor starves part of the bundle, which shows up as an uneven wiping pattern between tube zones in the same water box.

3. Ball Size, Ball Quantity and Dosing Parameters

Ball diameter sets the wiping force. Wet diameter runs 1-2 mm above the tube bore, so a φ25 x 0.5 mm titanium tube takes a φ26-φ27 wet ball; undersize balls will not bear on the wall and oversize balls jam in the water box and at tube inlets. The field check is a trial pass: a ball that is carried through the bundle and leaves a wiping mark on the tube wall is the right size.

Ball quantity sets how continuous the wiping is. Size the charge at 10-15% of the tubes in one pass, taking the lower end for short bundles and the upper end where tubes are long or circulating water turbidity is high. A bundle that is never reached cannot be wiped once an hour, and a short charge shows up as an end difference that comes down slowly and never settles. Balls are normally abrasion-resistant rubber with a density close to that of water, so balls that sink or float in front of the tubesheet mean the density is wrong.

Dosing parameters decide whether the effect holds. The usual practice is 2-4 dosing runs per shift of 30-60 min each, and units with persistently high circulating water turbidity can dose continuously at low output. Dosing rate - dosing time as a share of unit running time - stays at 95% or above, and recovery at 90% or above, both logged once per shift and compared month on month.

4. Day-to-Day Operation: Working Through the Recovery Rate

Set the records up first: dosing window, balls charged, balls recovered, pump discharge pressure and screen differential, five items per shift. With the data in hand there is an order to work in; on most sites the problem is not that the fault cannot be fixed but that nothing is logged and the judgement is made by feel.

When recovery goes wrong, run one fixed order: ball diameter, ball quantity, collection screen, pump and valves, distributor. Check whether the balls have worn undersize or broken balls have got into the charge; check the actual charge against the design figure; open the collection screen and look for deformed mesh or torn panels, both of which pass balls through; confirm pump discharge pressure and valve positions; only then touch the distributor. Worked in that order, the fault is usually located within two or three shifts.

5. Sequencing Against Shutdown Chemical Cleaning and Water Jetting

During chemical cleaning the balls must all come out, with the collection screen and charging chamber emptied as well. Cleaning liquor swells the rubber and is absorbed by it, and a ball jammed at a tube inlet disturbs the flow distribution in the cleaning circuit and shortens ball life; this is the step most often missed on units where the cleaning and the dosing have to be squeezed into a short shutdown window.

The recovery sequence after cleaning runs: tube-by-tube water jetting, or completion of rinse and displacement after the chemical clean, then a trial pass to confirm no jams, then back into service within 3 days with the starting recovery rate logged. The trial pass is not optional: if scale fragments or cleaning debris are left in the bundle, the first proper dosing run will jam balls at the inlets and put the end difference into oscillation.

Circulating water treatment has to be part of the same plan. Keep the cycles of concentration and the turbidity under control, because ball consumption multiplies on units where turbidity stays high; scale inhibitor and rubber balls are complementary, the inhibitor slowing new deposit formation and the balls removing soft deposit that has already attached. With both in place the ball system is what stretches the cleaning interval.

6. Case Study: Retrofitting the Ball System on a 300 MW Unit

In June 2026 we retrofitted and commissioned the rubber ball cleaning system on a 300 MW unit at a thermal power plant in East China. The condenser is a two-pass surface type with about 18,000 m2 of cooling surface and some 24,000 titanium tubes of φ25 x 0.5 mm, on once-through circulating water. Before the work the system ran a dosing rate of 62% and a recovery rate of 71%, the end difference sat between 7.5 and 8.0 C, the cleanliness factor was 0.71, and ball consumption was about 300 a month.

Three faults came out of the survey. The original charge was φ25 and, after wear, the working balls were under φ24, so both wiping force and recoverability had dropped; the collection screen was still set for the old ball size and the mesh was already deformed; and the distributor was biased, with a visibly different wiping pattern in the two tube zones of the same water box. The retrofit replaced the screen (18 mm mesh for φ27 balls), re-checked the diameter at φ27, sized a charge of 1,400 abrasion-resistant balls at 12% of the tubes in one pass, repaired the distributor bias, and added a ball counter with a per-shift log sheet.

Three months after commissioning: dosing rate 96%, recovery steady at 93%, end difference back to 4.8 C, cleanliness factor 0.86, and ball consumption down to 90 a month. The unit had had a chemical clean the previous year, and at the present maintenance level the cleaning interval is expected to stretch from 8-10 months to 16-18 months. For route selection see condenser cleaning methods compared; the shutdown work is described in on-line non-stop chemical cleaning and copper tube condenser cleaning and inhibition.

7. Acceptance: System Performance and Cleaning Result Verified Separately

Acceptance runs on two tracks. The system track has four items: dosing rate at 95% or above, recovery at 90% or above, monthly ball consumption inside the normal band for the charge, and a trial pass with no jams; these are confirmed from the operating log and a site test, and they describe the capability of the system itself.

The cleaning track covers end difference, cleanliness factor and vacuum, all read after 72 h of continuous full-load operation, because readings taken just after start-up are not admissible. Quality is judged under GB/T 25146-2010, with scale removal not below 95% for carbonate scale and slime and not below 85% for other deposit types, and same-material coupons used where a corrosion rate has to be established. Beyond the two tracks there is one further check: dosing must not import corrosion or wear, since titanium tubes are commonly 0.5-0.7 mm wall and oversize or over-hard balls wear the bundle as surely as scale does.

8. Frequently Asked Questions

Can rubber ball on-line cleaning replace chemical cleaning?

No. Rubber balls wipe off soft deposits, slime and biofilm that have just attached; once a carbonate layer above 0.3 mm has formed, the ball bounces off the tube inlet and the recovery rate falls with it. The correct order is to remove hard scale first by chemical cleaning or water jetting, then hand the bundle back to the ball system for maintenance.

What wet ball diameter should be used on a 25 mm tube?

Take the tube bore and add 1-2 mm, so a φ25 x 0.5 mm titanium tube runs a wet ball of φ26-φ27. The field check is a trial pass: the ball should be carried through the bundle by the water while leaving a wiping mark on the tube wall. Replace or top up balls that have worn more than 1 mm off nominal diameter.

Where do we look first when the recovery rate drops below 80%?

Work in this order: ball diameter, then ball quantity, then the collection screen, then pump and valves. Check whether the balls have worn undersize or the charge is short - 1,400 balls for 12,000 tubes in one pass is a common figure on a 300 MW unit - then inspect the screen for deformed or torn mesh, and confirm pump discharge pressure and valve positions. On the case unit, re-checking the diameter from φ25 to φ27 and repairing the distributor brought recovery back from 71% to 93%.

Must the balls be taken out during chemical cleaning?

Yes, all of them, with the collection screen and charging chamber emptied as well. Cleaning liquor swells the balls and is taken up by the rubber, and a ball jammed at a tube inlet both disturbs flow distribution in the cleaning circuit and shortens ball life. Once cleaning is finished and a trial pass has confirmed no jams, put the system back into service within 3 days and log the starting recovery rate.

How long does a rubber ball system take to bring the end difference back?

With the system dosed properly, a trend shows in 2-3 weeks and a stable figure is read at 3 months. On the case unit the dosing rate rose from 62% to 96% and recovery from 71% to 93%; over 3 months the end difference came back from 7.5-8.0 C to 4.8 C, the cleanliness factor from 0.71 to 0.86, and ball consumption fell from about 300 to 90 balls a month.

All cleaning processes and acceptance criteria in this article follow GB/T 25146-2010 Quality acceptance specifications of chemical cleaning for industrial equipment and DL/T 957-2017 Guide for chemical cleaning and film formation of condensers in fossil fuel power plants.

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