Cooling procedure of the modern kraft recovery boiler
Wahlman, Toni (2022)
Diplomityö
2022
School of Energy Systems, Energiatekniikka
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Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi-fe2022111065088
https://urn.fi/URN:NBN:fi-fe2022111065088
Tiivistelmä
In recent years, the trend has been to reduce the shutdown time of the pulp mills by extending the operation periods and by shortening the duration of planned shutdowns. With this, it has become necessary to find more ways to shorten the duration of shutdown activities.
The purpose of this Master’s thesis is to find actions to speed up the cooling procedure of the modern kraft recovery boiler. The target of the study was achieved and needed actions to enable an efficient cooling rate of the recovery boiler are given in this Thesis. The cooling time can be shortened remarkably, and this enables earlier initiation of water washing of the boiler in the economizer area. Slow cooling of the smelt on the bottom of the furnace may delay the starting of the water washing of the furnace, superheaters, and boiler bank due to the risk of smelt water explosion.
The main principle of efficient cooling of the boiler is to utilize the ability of water vaporization to bind heat. Formed steam is then led out from the boiler to be utilized further in the mill processes. The cooling rate can be speeded up by increasing the mass flow of the main steam out from the boiler through the pressure reduction valves.
The impact of the air blown into the furnace has a much minor effect on the cooling process. The air blown into the furnace is first heated by convective heat transfer in the furnace, superheaters, and boiler bank area but in the economizers, part of the heat is captured back to the water circulation of the boiler. For this reason, the amount of outgoing heat bound to air is quite small.
The purpose of this Master’s thesis is to find actions to speed up the cooling procedure of the modern kraft recovery boiler. The target of the study was achieved and needed actions to enable an efficient cooling rate of the recovery boiler are given in this Thesis. The cooling time can be shortened remarkably, and this enables earlier initiation of water washing of the boiler in the economizer area. Slow cooling of the smelt on the bottom of the furnace may delay the starting of the water washing of the furnace, superheaters, and boiler bank due to the risk of smelt water explosion.
The main principle of efficient cooling of the boiler is to utilize the ability of water vaporization to bind heat. Formed steam is then led out from the boiler to be utilized further in the mill processes. The cooling rate can be speeded up by increasing the mass flow of the main steam out from the boiler through the pressure reduction valves.
The impact of the air blown into the furnace has a much minor effect on the cooling process. The air blown into the furnace is first heated by convective heat transfer in the furnace, superheaters, and boiler bank area but in the economizers, part of the heat is captured back to the water circulation of the boiler. For this reason, the amount of outgoing heat bound to air is quite small.