coal power plant slagging

Slag after using PentoMag® 2550

| The trial started on 31.10.2014 after commissioning of a dosing installation.

| The initial dosing rate was set up as 1 liter/50 tons of coal.

During this period, coal for combustion was delivered mainly from mine with low ash melting temperature which causes slagging of boiler heating surfaces, increase of primary and secondary steam temperature as well as the full opening of spray water injectors to primary and secondary steam.

This kind of operation of a boiler causes problems with too high metal temperatures on individual steam superheaters.Moreover, it is very non-economic due to using water injections and due to the necessity of boiler load reduction.

An additional aspect is too high flue gas temperature in the area of SCR, which also causes a necessity of reducing the power.The issues described above have been limited while using Pentomag 2550.

Partial self-cleaning of heating surfaces of the boiler was noticed (especially evident as periodic collapsing of slag buildups from the heating surfaces).

Due to the above-mentioned phenomenon, an increase of the dosing rate up to 1 liter/45 tons was recommended.A compact dosing installation enabled to perform a very precise dosing, with accuracy up to 0.5% with reference to the amount of coal being burned. The antislagging additive PENTOMAG 2550 enabled self-cleaning of the boiler and protected superheaters metals from an excessive increase of temperature.The examples from boiler 11 dated on 29.11.2014 showing that after cleaning of boiler surfaces the temperatures on metal decreased about 50 °C and the temperatures on steam decreased about 10 to 15 °C.It helps to reduce the flow of spray water injection and to improve the boiler efficiency.The additive used has also impact on the structure of hanging deposits being created inside the firebox.Before using Pentomag 2550, inside the firebox liquid slag was flowing down the boiler water walls.

Slag before using PENTOMAG 2550

Slag before using PENTOMAG 2550

This slag, after collapsing from the walls, created a very difficult to be crushed/crumbled glassy structure.

Moreover, when the boiler was out of operation the slag residuals were present inside the firebox.
At boiler bridge zone a radiant superheater was found to be covered with not only dust but also with agglomerated slag.

Slag after using PENTOMAG 2550

After using the antislagging additive, slag buildups inside the firebox changed its character.

Instead of glassy “lava” flowing down on the surface of water wall pipes, solid deposits with tendency to peel off from the walls are created.
This new deposits have a very friable and porous structure. After boiler shutdown, self-cleaning of the surfaces was observed – the slag deposits have been peeling off.
There was no signs of sinter deposits inside the firebox.
Slag structure before

Slag before using PENTOMAG 2550

Slag before using PENTOMAG 2550

This slag, after collapsing from the walls, created a very difficult to be crushed/crumbled glassy structure.

Moreover, when the boiler was out of operation the slag residuals were present inside the firebox.
At boiler bridge zone a radiant superheater was found to be covered with not only dust but also with agglomerated slag.
Slag structure after

Slag after using PENTOMAG 2550

After using the antislagging additive, slag buildups inside the firebox changed its character.

Instead of glassy “lava” flowing down on the surface of water wall pipes, solid deposits with tendency to peel off from the walls are created.
This new deposits have a very friable and porous structure. After boiler shutdown, self-cleaning of the surfaces was observed – the slag deposits have been peeling off.
There was no signs of sinter deposits inside the firebox.

SUMMARY

A trial from using PENTOMAG 2550 at coal-fired power plant proved a positive impact of the additive on boilers operation, especially when burning slagging coal i.e. coal with low ash melting temperature.
The additive effectively prevents creating of the deposits inside the boiler

also when co-combustion of coal with over 5% share of biomass, in relation to high amount of chlorine in biomass.

The use of the additive significantly protects the heating surfaces via preventing of deposit formation.

Thanks to this, the following negative aspects can be avoided:

  • the significant increase of metal temperature, which causes the necessity of full spray water injection to the boiler;
  • improper heat exchange between flue gas and heat exchangers, which causes an increase of flue gas temperature at the inlet of catalyst above acceptable value and forces the boiler operator to lower the power unit load;
  • the excessive heat load of the radiant superheaters III0 and V0 which causes an increase of primary and secondary steam temperatures as well as a decrease of boiler power due to protection measures;
  • the necessity of mechanical cleaning (or even hammering) of sintered slag inside the firebox.

The additive prevented excessive formation of slag material which causes the above-described effects inside the boiler.

Undoubtedly, the additive has to be used when:

  • slagging coal is burned;
  • co-combustion with more than 5% of biomass takes place;
  • coal (from stockyard) of unknown origin is burned;
  • when first symptoms of slagging occur.

When it comes to the principle of continuous dosing of coal additive, it would need further investigation with and without using the additive when non-slagging coal is continuously burned and while co-combustion with biomass share below 5%.
The amount of additive and specifics of coal delivery did not allow to perform such analysis in this special case.

Interior of the firebox with slag deposits, when antislagging additive not used.

Interior of the firebox with slag deposits, when antislagging additive not used.

A view of the boiler with build-up on a radiant super heater

A view of the boiler with build-up on a radiant super heater
Interior of the firebox with slag

Interior of the firebox with slag deposits, when antislagging additive not used.

Interior of the firebox with slag deposits, when antislagging additive not used.
Build-up on a radiant super heater

A view of the boiler with build-up on a radiant super heater

A view of the boiler with build-up on a radiant super heater

Used product(s)