Heat recovery surfaces arrangement in a recovery boiler

An arrangement in a chemical recovery boiler having a furnace for combusting waste liquor and a flue gas duct comprising vertical flue gas channels, at least part of which are provided with heat recovery units for recovering heat from flue gases, wherein said heat recovery units comprise heat surface elements,

• wherein within a first flue gas channel after the furnace are a superheater and a secondary heat recovery unit, an open gas passage and an upper outlet, such that the flue gasses flow through the first flue gas channel sequentially downwards through the superheater and the secondary heat recovery unit, upward through the open gas passage, and through the upper outlet to a next one of the vertical flue gas channels,
• wherein the secondary heat recovery unit is at least one of:
• an economizer, a boiler bank and a reheater, and
• heat surface elements of the superheater are positioned side-by-side with heat surface elements of the secondary heat recovery unit along a direction transverse to a horizontal incoming direction of the flue gas, and
• the heat surface elements of the superheater and the heat surface elements of the secondary heat recovery unit are positioned parallel to a flow of the flue gas flowing in the first flue gas channel such that flue gas heats the superheater and the secondary heat recovery unit simultaneously,
• wherein the secondary heat recovery unit is disposed entirely in the first flue gas channel.

A chemical recovery boiler comprising:

• a furnace configured to combust waste liquor and direct flue gases upward;
• a bank of superheaters arranged in an upper region of the furnace;
• a flue gas duct adjacent and horizontally offset from the bank of superheaters, wherein the flue gas duct is configured to receive the flue gasses flowing from the bank of superheaters and the flue gas duct includes:
• flue gas channels arranged vertically in the flue gas duct and each of the flue gas channels having an upper inlet configured to receive the flue gasses, an ash hopper at a bottom portion of the flue gas channel, a heat recovery unit oriented vertically in the flue gas channel, and an open gas passage extending from the ash hopper to an upper outlet of the flue gas channel, wherein the heat recovery unit is upstream of the open gas passage along a gas path through the flue gas channel;
• and
• a first flue gas channel of the flue gas channels having the upper inlet to receive the flue gasses directly from the bank of superheaters and wherein the heat recovery unit in the first flue gas channel includes a superheater and a secondary heat recovery unit which is at least one of an economizer, a boiler bank and a reheater;
• wherein the gas path through the first flue gas channel flows simultaneously through the superheater and the secondary heat recovery unit, and
• wherein the secondary heat recovery unit is disposed entirely within the first flue gas channel.

A chemical recovery boiler comprising:

• a furnace configured to combust waste liquor and direct flue gases upward, wherein vertically oriented walls of the furnace include wall tubes;
• a bank of superheaters arranged in an upper region of the furnace;
• a steam drum external to the furnace and having an outlet for water which provides water for the wall tubes;
• a first flue gas channel adjacent and offset along a horizontal direction from the bank of superheaters, wherein the first flue gas channel is oriented vertically, is defined by walls of the first flue gas channel, has an upper inlet configured to receive the flue gases flowing from the bank of superheaters, has an upper outlet for the flue gasses and has a bottom ash hopper;
• a heat recovery unit entirely disposed within a region of the first flue gas channel in which the flue gasses flow downward from the upper inlet towards the bottom ash hopper, wherein the heat recovery unit is separate from the walls of the first flue gas channel and spans a width of the first flue gas channel and the heat recovery unit includes a superheater and a secondary heat recovery unit which is at least one of an economizer, a boiler bank and a reheater and wherein the first flue gas channel is configured to guide flue gases simultaneously through the superheater and the secondary heat recovery unit;
• and wherein the first flue gas channel includes an open gas passage in which the flue gasses flow from the heat recovery unit in an upward direction to the upper outlet, and
• a second flue gas channel oriented vertically and having an upper inlet configured to receive the flue gasses flowing from the upper outlet of the first flue gas channel.