| 摘要 |
<p>The invention relates to a process for recovering alkali and heat from a black liquor (5) containing silicate from a soda cook of e.g. grass, reed, straw and bagasse. In the process the black liquor (5) is treated with a gas (6) containing carbon dioxide to precipitate silica and lignin, the precipitate (9) is separated (2) from the black liquor, which is evaporated (3) and burnt (4) to generate heat and to recover a sodium carbonate melt. In the invention the black liquor (5) containing silicate is neutralised with a surplus of the gas (6) containing carbon dioxide, which preferably contains over 60% by volume of carbon dioxide. The evaporation (3) of black liquor mainly takes place after the precipitate (9) rich in silica has been separated (2). The combustion is performed with pure oxygen gas or oxygen-enriched air (14), after the black liquor has been brought to a temperature near its boiling point by direct contact with the hot exhaust gases from combustion, all these operations under a substantial over-pressure of at least 100 kPa. With this procedure, a sodium carbonate melt is recovered and a gas (17) containing over 60% by volume of carbon dioxide is formed, which is used to neutralise the black liquor (5) containing silicate. <IMAGE></p> |
