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On each side of the combustion chamber in every boiler, an air-cooled selective slag cooler is installed to facilitate slag discharge from the boiler and maintain the bed pressure within a normal range. The bed material enters the slag cooler through pipes lined with refractory material; these pipes are equipped with high-pressure air nozzles, and the vibration generated by the high-pressure air in the inlet pipes causes the bed material to fall into the slag cooler. The cold slag chamber is divided into four chambers, namely the selection chamber, cooling chamber 1, cooling chamber 2, and cooling chamber 3. Each of the selection chamber and the lower part of the cooling chamber 1 is equipped with a blower, along with directional air nozzles; cooling chamber 2 and cooling chamber 3 share one blower, which is also fitted with directional air nozzles. Number of wind belts: 98 in Chamber 9, 123 in Cooling Chamber 1, 134 in Cooling Chamber 2, and 169 in Cooling Chamber 3. Cold primary air passes through the selector chamber bellows and directional air nozzles to first cool and separate the bed material entering the cold slag chamber; as a result, the fine particles together with the gas are returned to the furnace through the gas-solid outlet, while the remaining ash is directed to the cooling chamber 1. In cooling chamber 1, the cold primary air further cools the ash, which is then directed to cooling chamber 2. The cold primary air blown here enhances the cooling of the ash and slag, and directs it into the cooling chamber. The cooled primary air in the three-chamber cooler further cools the ash, which is then discharged from the ash cooler through the ash discharge port. The primary air flow rates for the selection chamber, cooling chamber 1, cooling chamber 2, and cooling chamber 3 are all measured by venturi flow meters and can be automatically adjusted via the DCS system. The slag cooler also has a gas return pipe connected to the furnace, through which the cooled gas returns to the furnace. The bottom ash discharged from the slag cooler passes through a gate valve, and is then conveyed by an electric feeder to a rotary sieve. After screening (with the maximum particle size at the sieve outlet being 10 mm), it drops into a buffer hopper, where it is temporarily stored. Subsequently, it is transported pneumatically (using dense-phase pulses) to the common bottom ash storage tank for both furnaces via a bottom ash conveyor (silo pump). This bottom ash storage tank is a steel structure with a diameter of 10.8 m, a height of 29.5 m, and a volume of 1000 m3. The top of the tank is equipped with an exhaust dust collector and a pressure relief valve, while manholes are located on the bottom side of the tank. Each slag cooler is equipped with an independent rotary sieve, a pneumatic conveyor, and conveying pipes. Each furnace is equipped with two slag coolers, hence there are two bottom ash systems, with a total output of 15 t/h.