Boiler Steam and Water Flow General Description

Feedwater enters the bottom header of the economizer (Fig. 2). The water passes upward through the economizer and stringer tubes, and discharges through the outlet headers into piping which conducts the heated feedwater to the steam drum. The economizer stringers support the primary superheater as well as transport water to top of the boiler. The heated (but still subcooled) feedwater mixes with saturated water already in the drum. This subcooled mixture flows down through the four (4) downcomer pipes and is distributed to the various furnace lower headers by supply pipes. From the furnace wall headers, the fluid rises by means of natural circulation, through the furnace wall tubes to the upper enclosure headers.

The water/steam mixture leaving the furnace then passes through riser tubes into the steam drum (Fig. 3 Furnace Circuitry). The saturated steam/water mixture enters the drum beneath the manifold baffle plates (Fig. 4 Cyclone Separators and Steam Scrubbers). This mixture flows between the baffle plates and the drum shell into the cyclone separators. The essentially steam free saturated water exits the cyclone through the bottom and mixes with subcooled feedwater. This mixture flows through the vortex eliminators into the downcomers. The steam leaving the cyclones passes through first primary then secondary scrubbers and is delivered as at least 99% pure steam. Fig.4 Shows a typical drum with internals.

Fig. 2 RBC Boiler Superheater, Reheater & Econ. Circuitry

Fig. 2 RBC Boiler Superheater, Reheater & Econ. Circuitry

The saturated steam leaving the drum (Fig. 5) is routed to the roof inlet header and then flow to the front wall upper header. From this header some of the steam flows across the roof and down the enclosure rear wall to the rear wall lower header. From the rear wall lower header some of the steam flows through connecting tubes to the baffle wall lower header, then across the lower baffle wall to the primary superheater inlet header. Some of the steam from the rear wall lower header flows through connecting tubes to the horizontal convection pass enclosure (superheater path) lower header, up the horizontal convection pass enclosure, then through connecting tubes to the baffle wall upper header, and down the upper baffle wall to the primary superheater inlet header.

Some of the steam from the front wall upper header flows down the horizontal convection pass front wall to the front wall lower header. From the front wall lower header some of the steam flows through connecting tubes to the pendant convection pass enclosure, then through connecting tubes to baffle wall upper header, down the upper baffle wall to the primary superheater inlet header. Some of the steam from the front wall lower header flows through connecting tubes and across the horizontal convection pass enclosure, through connecting tubes to the baffle wall upper header, then down the upper baffle wall to the primary superheater inlet header.

Steam flow rises through the primary superheater and discharges through both end outlet header and through connecting piping along each side through first stage spray attemperators (Fig. 2). From both ends, the steam enters the platen inlet header. After flowing through the platen sections, it discharges from both ends of the platen outlet header. After passing through the second stage attemperators located in the platen to secondary superheater connecting pipes, the steam enters the secondary superheater inlet header and flows through the secondary superheater sections to the outlet header and to discharge pipes which terminate.

The spraywater for the superheater and reheater attemperators will be sourced from the area of the feedpump discharge ahead of the high pressure feedwater heaters. This is done in order to have a lower temperature spray source to reduce the quantity of spray required and to have additional pressure in the spray system to eliminate the need for throttling of the feedpump at full load.

Steam returning from the turbine passes through the reheat attemperators located in the inlet piping to the reheat superheater. It then flows through the reheat superheater sections to the outlet as shown on Fig. 2.

Fig. 3 Furnace Circuitry

Fig. 3 Furnace Circuitry

Fig. 4 Cyclone Separators and Steam Scrubbers in Steam Drum

Fig. 4 Cyclone Separators and Steam Scrubbers in Steam Drum

Fig. 5 Downshot RBC Boiler Convection Pass Circuitry (parallel Downpass)

Fig. 5 Downshot RBC Boiler Convection Pass Circuitry (parallel Downpass)

 

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