Abstract: The present invention pertains to a reactor for producing sodium or potassium silicate. The reaction vessel includes submerged burners. A trough extends downwards and away from the reaction vessel. The trough connects to an outlet in the reaction vessel where molten silicate produce is removed, molded, and allowed to cool. The reactor also includes first and second heat exchangers, both located in the exit path of the exhaust gases from the reactor. The exhaust gases pass through a first heat exchanger and exchange heat with incoming combustion gas. This preheated combustion gas is then used as the oxidizer to burn fuel gas through the burners. The hot exhaust gases are then passed through a second heat exchanger. The second heat exchanger exchanges heat between the hot flue exhaust gases and feed sand. The hot exhaust gases can also be passed through a third heat exchanger to make hot water. The hot water is used to dissolve the silicate product.