Help after unintentional oil leakage in a steel mill cooling circuit

Initial situation

There was a mas­sive and con­tin­u­ous oil intru­sion into the cool­ing sys­tem via an oil-water heat exchang­er in a steel mill cool­ing cir­cuit. There was no way to repair the heat exchang­er until a planned shutdown.

The cool­ing water showed an increased milky (emul­sion) tur­bid­i­ty, and the water sur­face was oily. The oil intru­sion could also be doc­u­ment­ed by an increase in the COD value.

There was a risk that the entire cool­ing sys­tem would become sludged with oil. This also affect­ed the cool­ing tow­er inter­nals, which had just been new­ly installed 3 months ear­li­er. The cool­ing effect in oth­er heat exchang­er process­es could also be reduced by oil deposits. In addi­tion, increased micro­bi­o­log­i­cal con­t­a­m­i­na­tion had to be expect­ed, since the oil served as food for the microbiology.

Concept of INWATEC

Since there was no pos­si­bil­i­ty to repair the heat exchang­er and there were no fil­tra­tion pos­si­bil­i­ties in the cool­ing sys­tem, the only pos­si­bil­i­ty to quick­ly pro­vide an improve­ment in the cool­ing sys­tem was to keep the oil in the water with the help of a dis­pers­er and to get it out of the cool­ing sys­tem via an increased drainage.

For this pur­pose, the INWASIL D‑4100 oil dis­pers­er, an Inwa­tec devel­op­ment for foundry cool­ing sys­tems in the alu­minum indus­try, was used at a con­cen­tra­tion of 50 mg/l.

The effec­tive­ness of the oil dis­per­sant was doc­u­ment­ed using the COD con­tent in the cool­ing water. This should increase when oil is addi­tion­al­ly dis­persed into the water.

Results

The oil dis­per­sant was first dosed in the surge to quick­ly reach the tar­get con­cen­tra­tion. No foam­ing was reg­is­tered in the cool­ing sys­tem. Then, the prod­uct was dosed con­tin­u­ous­ly with a dos­ing pump to com­pen­sate for loss­es due to runoff.

The oil dis­per­sant was dosed for approx­i­mate­ly 20 days. The planned shut­down and clean­ing of the cool­ing sys­tem took place 5 days after the start of dosing.

The COD val­ue was 730 mg/l before the start of dos­ing from the oil dis­per­sant. This is a sig­nif­i­cant­ly ele­vat­ed val­ue. In cool­ing sys­tems with indi­rect cool­ing, the COD is usu­al­ly 20 — 50 mg/l.