How is the setting of bricks done in an Induced Draught Zigzag Kiln (IDZK)? [Brick setting type-2]
In an Induced Draught Zigzag Kiln (IDZK), the setting of bricks is different from that in a Fixed Chimney Bull's Trench Kiln (FCBTK). This Knowledge Brief discusses a triple zigzag brick setting widely practised in the northern part of India. Another Knowledge Brief, titled - How is the setting of bricks done in an Induced Draught Zigzag Kiln (IDZK)? [Brick setting type-1], discusses the single zigzag brick setting, which is widely practised in eastern India.
How is the brick setting different in an IDZK compared to that in an FCBTK?
In an FCBTK, bricks are stacked in vertical columns in a line (row) across the width of the trench. The rows of brick columns are arranged one after the other in the direction of air flow.
In an IDZK, bricks are stacked in such a manner that distinct chambers of brick setting are formed in the kiln. Just like in the case of FCBTK, in IDZK also, the bricks are stacked in vertical columns in a line (row) across the width of the trench. However, unlike in FCBTK, all the brick columns are not of the same width. The rows of brick columns are arranged one ahead of the other in the forward direction of fire travel. In an IDZK, one chamber of brick setting consists of six such rows.
Because of different brick settings, the path of air flow in the two kilns is also different. In an FCBTK, the air flows in a straight-line path along the length of the trench. In an IDZK, the air flows both across the width and along the length of the trench in a zigzag path. How the air is made to follow a zigzag path is explained in detail later in this Knowledge Brief.
What is the size of a chamber in an IDZK?
Chamber dimensions are fixed in the following way:
- The width of a chamber is equal to the width of the trench.
- The length of a chamber depends on the size of the brick. One chamber consists of six rows/lines of bricks. The thickness of each row is equal to the length of a brick. A gap of about half a brick length is left between two consecutive rows. The length of a chamber usually varies between 6 and 7 foot (1.82–2.13 m).
How are bricks arranged in a chamber in an IDZK?
In a chamber, bricks are arranged according to the following method:
- Generally, bricks are arranged in a chamber in six lines/rows consisting of one ‘end row’ and five ‘middle rows’. The thickness of each row is equal to the length of a brick. A gap of about half a brick length is left between two consecutive rows.
- Middle rows of the chamber consist of several columns of bricks. All columns, except two columns adjacent to the walls, in a row are of the same size in a Zigzag Kiln.
- The last row (sixth row) of the chamber is like a brick wall with a few openings left for the flow of air/hot gases.
- The number and size of columns depend on the production capacity of the kiln and the width of the trench.
- Adjoining rows are joined together by bricks, called bandhan, at multiple levels to make the brick setting structurally stable.
- Adjoining columns of a row are joined together by a pair of bricks, called jodi, at multiple levels to make the brick setting structurally stable and during firing, to give fuel space to be lodged onto them.
How are the openings for air-flow at the end of a chamber arranged in an IDZK?
In the last row in each chamber (in the direction of air flow), i.e., the chamber walls, a set of two to three openings adjacent to Miyana/outer wall and, a set of four to six openings adjacent to the mid-plane of the chamber are made. Number of openings in the set adjacent to the mid-plane must be even in number. In the set of gaps near the walls, number of openings must be half the number of openings adjacent to the mid-plane. In a given chamber wall, these two sets of gaps are made on opposite sides of the mid-plane. In the next chamber these sets of gaps interchange their sides with respect to the mid-plane. In this way these sets of gaps interchange their position turn by turn in the upcoming chambers.
This arrangement of openings in the chambers results in the zigzag flow of air and is repeated throughout the length of the rectangular trench.
How is the air made to follow a zigzag path in an IDZK?
As shown in the above diagram, the openings in the wall of a given chamber are not in-line with the openings in the wall of the last chamber. This staggered arrangement of gaps in the chamber wall ensures that air/hot gases entering through the openings near the Miyana/outer wall flow towards the middle to be exited through the gaps left adjacent to the mid-plane of the chamber. Similarly, part of air/hot gases entering through the gaps near the middle will flow towards the Miyana or outer wall to be exited through the gaps left at the corner of the chamber.
This Zigzag flow pattern is repeated in alternating chambers throughout the length of the rectangular trench.
How is the brick setting done in the Gully region of an IDZK?
The zigzag brick setting is done only in the longer lengths of the rectangular trench. In the shorter lengths of the rectangular trench, which is called gully, brick setting is done as in FCBTK.
In the gully region (shorter length of the rectangular trench), all the rows, except the last row, are made of equally spaced same size brick columns in exactly the same way as in an FCBTK. Air flows in a straight-line path in this region. At the entry and the exit of the gully region, the openings are left only near the outer wall end of the trench. This arrangement ensures that the air also flows through the extreme corner of the trench thereby exchanging heat with as many bricks as possible. The openings at only the outer wall end also prevent short-circuiting of the air flow near the Miyana of the kiln.