Pulverizer having rotatable grinding table with replaceable air port segments

Abstract: A pulverizer for particulate material such as coal includes a housing (12) having a centrally located feed chute (24), and encloses a rotary grinding table (14) having an air port unit formed as multiple segments (32) removably attached to the rotary table outer periphery and containing air flow passageways. Located adjacent the air port unit is an outer segmented ring (40) attached rigidly to the pulverizer housing, with a radial gap (42) being provided between the outer ring and the air port unit ring segments (31). The outer ring segments include upper wear plugs (41) removably attached onto the outer ring lower segments (40a). Whenever the upper parts (31a) of the air port unit segments become worn excessively due to erosion, or there is a need to change air flow requirements of the pulverizer, the rotatable air port segmented ring upper parts (31a) only are conveniently replaced along with the upper wear segments (41) of the adjacent outer stationary ring.

Description: This invention pertains to pulverizers of the roll and race type which have a rotatable grinding table containing air port flow passages. It pertains particularly to such pulverizers for coal having a grinding table with multiple replaceable air port segments provided at the table periphery adjacent an outer segmented ring. Pulverizers for coal having a centrally located coal feed conduit and a rotary grinding table and rolls provided in the pulverizer lower portion for pulverizing coal and pneumatically conveying it upwardly to boilers for combustion therein are well known. For example, such pulverizers for coal are disclosed by US-A- 4 264 041 to Kitto, Jr. et al and US-A- 4 687 145 to Dougan et al. In these pulverizers, the carrier air passes upwardly from a plenum through air ports containing a plurality of vanes and entrains pulverized coal upwardly from the outer edge of the rotatable grinding ring. However, problems have been experienced with excessive wear in the pulverizer rotatable grinding table outer air port region near the pulverizer housing wall, requiring frequent replacement of large and expensive grinding table parts. Such excessive wear has occurred in the area between the rotating grinding table and the stationary airports, which has required frequent replacement of the airports. Also, the prior stationary air port designs promoted areas of excessive wear on the pulverizer housing and other internal components. US-A- 4 752 037 shows a pulverizer with air ports defined between an outer, stationary segmented ring and an inner segmented assembly fixed to the rotatable table. When the inner segments wear, as is inevitable, then the whole segment of the inner assembly will need replacement. It is therefore an object of the invention to mitigate wear problems due to erosion by the coal in the grinding table air port region of the pulverizer. According to the invention there is provided a pulverizer for pulverizing particulate materials, including a housing, a grinding table rotatably mounted in the housing and having annular air port openings provided between the table and the housing, roller means contacting the grinding table upper surface for pulverizing the particulate material thereon, an outer segmented ring attached to the housing inner wall at a location opposite the grinding table, and an inner segmented ring removably attached to an outer peripheral surface of the grinding table, so as to provide a narrow radial gap between the segmented outer ring and the segmented inner ring, characterised in that the inner ring segments include a lower part, removably attached to the grinding table outer periphery and having upright flow passageways therein, and an upper part, also removably attached to the outer periphery of the grinding table in an overlapping arrangement with the segment lower parts, each upper part having a plurality of upright flow passages therein, whereby the ring segment upper parts can be removed and replaced independent of the segment lower parts. A pulverizer according to the invention can pass primary air to pulverized material and pneumatically convey the material such as coal upwardly to a boiler for combustion therein. This invention advantageously provides a pulverizer having an air port unit for which the ring segments upper part, which receive the most erosion war, can be replaced easily and economically without requiring replacement of the entire air port assembly. The air port configuration also advantageously provides for changes in air flow requirements as needed to meet changes in pulverizer operations. Preferably the air flow passageways provided in the inner ring segments are angled radially inwardly at an angle of 10 to 20° relative to a vertical plane. Preferably also, the flow passages are angled forwardly relative to the intended grinding table direction of rotation at an angle of 40 to 60° and preferably at about 45° angle with the horizontal plane. The use of a 40 to 60° forward angle as compared to a smaller angle of about 30° results in less direct impingement if the entrained coal stream against the housing, which reduces housing erosion. The radial gap between the stationary outer segmented ring which is rigidly attached to the inner wall of the pulverizer housing and the air port rotatable inner ring segments is desirably from 0.100 to 0.190 inch (approx. 2.54 to 4.83mm) and preferably about 0.125 inch (approx. 3.175mm). The outer ring includes multiple segments, and preferably each segment has a lower part rigidly attached to the housing wall as by welding, and an upper part removably attached to the outer ring segment lower part such as by bolting. By utilizing this improved air throat configuration, whenever excessive wear occurs to the air port segment upper parts and to the upper parts of the outer ring segments, these upper parts can be conveniently removed and replaced without requiring replacement of the segmented lower parts which are larger and more expensive. Also, use of the separate segment upper parts allow these parts to be easily adjusted to maintain the desired 0.100 to 0.190 inch (approx. 2.54 to 4.83mm) radial gap between the air port rotating and stationary parts. The use of air port ring multiple segments having replaceable lower and upper parts according to the invention provides an improved means for matching of the pulverized air port air flow requirements to a particular pulverizer installation. Specifically, this configuration permits the air port lower segments to be sized to accommodate the largest volumetric air flow for a given pulverizer housing size, and permits the segments upper parts to be sized to provide a desired smaller air flow rate as required to attain the proper air velocity for upward coal transport desired for the particular pulverizer installation. As a result, if the coal properties change, only the upper parts of the air port segments would need to be replaced to maintain optimum coal transport air velocity, rather than replacing the entire airport assembly. Thus, the air port ring segment upper parts openings have flow passages which have between about 50 to 100% of the cross-sectional area of the ring segment lower parts. An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows an elevational sectional view of a coal pulverizer, including a rotary grinding table provided in the pulverizer housing lower portion; Figure 2 is a sectional plan view taken at line 2-2 of Figure 1 and showing a plan view of the grinding table; Figure 3 shows a vertical sectional view taken at line 3-3 of Figure 2; and Figure 4 shows a vertical sectional view taken at line 4-4 of Figure 2 and showing the air port flow passages. As in generally shown in Figure 1, a coal pulverizer assembly 10 includes an outer casing 12 which encloses a rotary grinding table 14. The grinding table 14 is supported by rollers in a stationary base structure 16, and is rotatable by a pulverizer gear reducer and drive motor 18 within the base 16. Triple equally spaced rollers 20 are pivotably attached to the housing 12 above the rotary grinding table 14. Rollers 20 can each rotate about their own shafts 21 which are pivoted at 22 to housing 12, so that the rollers 20 are each rotated in race 15 and on the coal therein by the rotation of the grinding table 14. The coal feed enters the pulverizer via a central downcomer unit 24 and falls onto a central portion 14a of the rotatable grinding table 14. The three rotatable grinding roller units 20, each of which rests on the grinding table race 15 and the coal therein, progressively crushes the coal particles as they are passed radially outwardly across the grinding table 14 towards a plurality of air ports 30 attached to the periphery of the table 14. Air provided from inlet conduit 26 and plenum 27 flows uniformly upwardly through air ports 30 to carry the pulverized coal particles upwardly to the pulverizer classifier vanes 28 and upper exits 29 to a combustion zone. A plan view of the pulverizer rotatable grinding table 14 and multiple air ports 30 is shown by Figure 2. It is seen that the multiple peripheral air ports 30 are provided by a segmented ring 32, which is rigidly attached to the periphery of the grinding table 14. The multiple air ports 30 are provided circumferentially spaced apart in the segmented ring 32, which is removably attached to the periphery of grinding table 14 such as by bolting. The segmented ring 32 contains multiple segments 31, with at lease 8 arcuate segments and usually not exceeding 20 segments being provided. As shown in greater detail by Figure 3, the multiple segments 31 of ring 32 are rigidly attached onto the outer periphery 14b of pulverizer grinding table 14. Each ring segment 31 consists of an upper piece 31a and a lower piece 31b. A multi-piece segmented retainer ring 34 is bolted to the periphery 14b of the grinding table 14 by bolts 35. Both the upper piece 31a and the lower piece 31b are bolted to the segmented retainer ring 34 using a staggered bolting arrangement of bolts 37a and 37b. A plurality of passageways 33 are provided through the ring segments 31, with the passageway walls being oriented radially inwardly by an angle A of 10 to 20° related to a vertical plane, and preferably at an angle of about 15°. If desired, a refractory cement material 39 can be provided in any gap between upper part 31a and rotatable table 14. An outer stationary ring 40 has a plurality of segments rigidly attached to the pulverizer housing 12 such as by welding, so as to provide a radial gap 42 between the outer ring 40 and the air port segmented ring 32. The radial gap 42 should be 0.100 to 0.190 inch (approx. 2.54 to 4.83mm) wide and is preferably about 0.125 inch (approx. 3.175mm) wide. A plurality of upper wear segments 41 are removably attached by bolts 43 onto the upper surface of the outer ring segments 40. The outer ring segments 40 consist of a plate 40b and cover 40a which are both welded together and also welded to the pulverizer housing wall 12. The segmented upper parts 41 are bolted onto the lower part cover 40a by at lease three spaced apart bolts 43 per segment. The outer stationary ring 40 includes at least 8 segments and usually not exceeding 20 segments. If desired, a refractory cement material 44 may be provided between the cover 40a and vertical plate 40b and housing 12. Also, a refractory cement material 45 may be provided between upper wear segments 41 and housing 12. The orientation and size of the air port flow passages 33 in ring 32 is further shown by figure 4. The flow passages 33 are all angled forwardly, i.e. in the direction of rotation of the grinding ring 14, by an angle B of 40 to 60° relative to a horizontal plane, and preferably by about 45° angle. The passages in the segmented ring lower pieces 31b are sized to accommodate the largest volumetric flow for a particular pulverizer frame size. The passages in the ring upper pieces 31a are sized to provide the proper air velocity for particulate coal transport based on the actual volumetric flow required for a particular pulverizer installation. As a result, the opening area in the upper pieces 3la are always equivalent to or smaller than the opening area in lower pieces 31b. It has been found that the total cross-sectional area of the flow passages 33 in the upper pieces 31a should be made 50 to 100% of the cross-section area of the flow passages in the lower pieces 31b. Thus, portions of the upper pieces 31a may overlap portions of the flow passageways in the lower pieces 31b, as in shown by Figure 4. By the arrangement, if fuel properties change and as a result the required volumetric air flow through the pulverizer also changes, the upper pieces 31a can be conveniently replaced to maintain optimum coal transport air velocity, rather than replacing the entire air port assembly. As the air port ring upper surfaces wear away due to erosion by the coal, only the top piece of plug 3la and outer upper wear segment 41 need to be replaced. With the prior art designs, the entire air port casting needed to be replaced, even though the erosion wear occurs only on the top surface of the ring. Pulverizer maintenance costs are thereby appreciably decreased because only the top wearing parts need to be replaced. Because the air port ring 32 is rotated with the grinding table 14, the air port housing wear is evened out and not confined to a few locations. Housing wear is further decreased by the use of a larger forward angle of inclination for the flow passages 33 of 40 to 60° and preferably about 45°, rather than a previously utilized 30° angle of inclination. Use of a two piece design for air port ring segments 31 also allows replacement of only the top pieces 31a of segmented ring 32 to maintain proper coal transport velocities in the event of a change in fuel properties. But with the prior art designs, the entire air port casting would need to be replaced in order to provide revised flow area for passageways 33 so as to maintain proper upward transport velocities for the crushed coal particles. This invention will be further described with the aid of the following Example, which should not be construed as limiting the scope of the invention. EXAMPLE A pulverizer for coal having a configuration generally as shown in Figure 1 was constructed having a segmented air port configuration. The air port included a segmented inner ring bolted onto the periphery of the grinding table and having a plurality of air passageways which are angled both inwardly and forwardly. The segmented inner ring included upper and lower parts each separately bolted onto a segmented retainer ring which is bolted onto the periphery of the grinding table. The air port also included a segmented outer ring, which had lower parts welded onto the pulverizer housing walls and upper parts bolted onto the lower parts. The air port segments had the following characteristics: Grinding table outer diameter - 120in (approx 3048mm) Number of inner ring segments - 15 Number of outer ring segments - 12 Radial gap between inner and outer rings - 0.125in (approx 3.175mm) Radial width of flow passages - 4in (approx. 101.6mm) Radial inward angle of flow passages - 15° Forward angle of flow passage - 45° Number of ports - 30 Whenever after extended service handling pulverized coal the upper parts of the air port ring segments become considerably worn, the upper parts only are removed from the grinding table inner ring and from the non-rotatable outer ring and are replaced with new parts.

Claims: A pulverizer for pulverizing particulate materials, including a housing (12), a grinding table (14) rotatably mounted in the housing (12) and having annular air port openings (30) provided between the table (14) and the housing (12), roller means (20) contacting the grinding table upper surface for pulverizing the particulate material thereon, an outer segmented ring (40) attached to the housing inner wall at a location opposite the grinding table (14), and an inner segmented ring (32) removably attached to an outer peripheral surface of the grinding table (14), so as to provide a narrow radial gap (42) between the segmented outer ring (40) and the segmented inner ring (32), characterised in that the inner ring segments (31) include a lower part (31b), removably attached to the grinding table outer periphery and having upright flow passageways (33b) therein, and an upper part (31a), also removably attached to the outer periphery (14b) of the grinding table (14) in an overlapping arrangement with the segment lower parts (31b), each upper part (31a) having a plurality of upright flow passages (331) therein, whereby the ring segment upper parts (31a) can be removed and replaced independent of the segment lower parts (31b). A pulverizer as claimed in Claim 1, in which the flow passageways (33a, 33b) are oriented radially inwardly at an angle of 10 to 20° relative to a vertical plane. A pulverizer as claimed in Claim 1 or Claim 2, in which the flow passageways (33a,33b) are oriented forwardly relative the intended direction of rotation of the table (14) at an angle of 40 to 60° relative to a horizontal plane. A pulverizer as claimed in any preceding claim in which the radial gap between the outer ring (40) and the inner ring segments (32) is 0.10 to 0.19 inches (approx. 2.54 to 4.83mm). A pulverizer as claimed in any preceding claim in which the cross-sectional area of the flow passages (33a) in the circumferentially spaced openings in the inner ring segment upper parts (31a) is 50 to 100% of the cross-section area of the flow passages (33b) in the inner ring segment lower parts (31b). A pulverizer as claimed in any preceding claim in which the inner ring segments (31a,31b) are bolted onto a segmented retainer ring (34), which is attached rigidly to the grinding ring outer periphery surface (14b). A pulverizer as claimed in Claim 5 in which portions of the inner ring segments upper parts (31a) overlap flow passages (33b) in the inner ring segments lower parts (31b), A pulverizer as claimed in any preceding claim in which such outer ring segment (40) includes an upper part (41) removably attached to a lower part (40a,40b).

Inventors: CUMMINS RALPH L, NOVOTNY RANDALL JOHN, CUMMINS, RALPH L., NOVOTNY, RANDALL JOHN
Applicants: FOSTER WHEELER ENERGY CORP, FOSTER WHEELER ENERGY CORPORATION
Application year: 1990
Main classification: B02C15
IPC codes: B02C15