Heat recovery from spent digester cooking liquor

A steam producing system for a cellulose pulp mill, comprising:

• a digester having a black liquor outlet;
• a heat exchange means having a hot liquid inlet, a hot liquid outlet, an evaporable liquid inlet, and an evaporable fluid outlet;
• said black liquor outlet connected to said hot liquid inlet;
• a source of evaporable liquid connected to said evaporable liquid inlet;
• means for producing steam from evaporable liquid introduced into said heat exchange means, and connected to said evaporable liquid outlet, and
• further comprising at least one flash tank connected to said evaporable fluid outlet, for flashing the evaporable liquid into steam;
• wherein said source of evaporable liquid comprises clean water, and wherein said heat exchange means comprises at least one liquid-to-liquid heat exchanger.

A steam producing system for a cellulose pulp mill, comprising:

• a digester having a black liquor outlet;
• a heat exchange means having a hot liquid inlet, a hot liquid outlet, an evaporable liquid inlet, and an evaporable fluid outlet;
• said black liquor outlet connected to said hot liquid inlet;
• a source of evaporable liquid connected to said evaporable liquid inlet;
• means for producing steam from evaporable liquid introduced into said heat exchange means, and connected to said evaporable liquid outlet, and
• wherein said at least one flash tank is at ground level.

A steam producing system for a cellulose pulp mill, comprising:

• a digester having a black liquor outlet;
• a heat exchange means having a hot liquid inlet, a hot liquid outlet, an evaporable liquid inlet, and an evaporable fluid outlet;
• said black liquor outlet connected to said hot liquid inlet;
• a source of evaporable liquid connected to said evaporable liquid inlet;
• means for producing steam from evaporable liquid introduced into said heat exchange means, and connected to said evaporable liquid outlet;
• wherein said means for producing steam comprises at least one flash tank connected to said evaporable fluid outlet, for flashing the evaporable liquid into steam;
• wherein said source of evaporable liquid comprises clean water;
• and wherein said heat exchange means comprises at least one liquid-to-liquid heat exchanger, and
• wherein said at least one flash tank is a retrofit to the pulp mill to replace an existing flash tank having a first size, and wherein said replacement flash tank has a size of at least about 50% smaller than the existing flash tank it replaced.

A steam producing system for a cellulose pulp mill, comprising:

• a digester having a black liquor outlet;
• a heat exchange means having a hot liquid inlet, a hot liquid outlet, an evaporable liquid inlet, and an evaporable fluid outlet;
• said black liquor outlet connected to said hot liquid inlet;
• a source of evaporable liquid connected to said evaporable liquid inlet;
• means for producing steam from evaporable liquid introduced into said heat exchange means, and connected to said evaporable liquid outlet;
• wherein said at least one flash tank is at ground level, and
• wherein said at least one flash tank is a retrofit to the pulp mill to replace an existing flash tank having a first size, and wherein said replacement flash tank has a size of at least about 50% smaller than the existing flash tank it replaced.