Venting dusts

Venting, dusts, (deflagration), nomograph, API, 514-520 Relief valves, 400 Code requirements, 415, 420 Installation, 422, 429-434 Safety-relief, 400 Relieving pressure, 411-417 Resistance coefficient, K, (flow), 71, 72 Flow coefficient, Q, 81, 83 Pipe sizing, 83, 84, 86 Sudden contraction, 80 Sudden enlargement, 80 Tables/charts, 73-76, 77, 78-80 Valves, 81... 

Additional dust explosion parameters can be measured (Pmax, maximum pressure a burning dust can generate and Kst, rate of pressure increase generated by burning dust), and these are typically used in the design of milling and dust collection equipment that is required to be able to withstand or vent dust explosions of varying severity. 

Three levels of plastic filler were examined for each of the tests 0, 1 and 4 percent by weight. Except for the vent dust and the HDPEfine, the rest of the fillers replaced 1 and 4 percent of the weight of the pea gravel. Vent dust and the HDPEfine substituted for the sand. Table 2 presents the plastic and the aggregate quantities used in mix No. 1 and No. 2. The cement factors and the water-cement ratios were given in Table 1. 

No noticeable segregation of the mix was found to be produced by the fillers. In fact, the cohesiveness of the mix was greatly improved with vent dust. During the mixing of the many batches none of the plastic fillers was observed to flow to the top. An analysis of the concrete samples showed that the mixing procedure had evenly distributed the plastic chips. 

If vent dust is excluded, one percent of plastic filler changed the strength from 110 percent (HDPEflake-1) to 92 percent (PS-1) of the control value. By incorporating 4 percent of plastic, the concrete strength varied from 99 percent (PET-4) to 82 percent (PVC-4) of the reference strength. 

The reason why vent dust reduced compressive strength 25 percent, with only a 1 percent plastic content, deserves a separate analysis. Two possible reasons for the low strength level are ... 

Vent dust reacted with part of the cement affecting thereby the subsequent hydration. This possibility could exist because of the presence of calcium carbonate (CaC03) and aluminum hydroxide (Al(OH)3) as components of the vent dust. 

One percent of polypropylene produced a concrete with lower impact resistance than plain concrete. When PP content was increased to 4 percent, the impact resistance improved to a level similar to plain concrete. Concrete with vent dust behaved similar to concrete with polypropylene. However, VD-4 modified concrete did not reach the level of plain concrete although PP-4 did. 

Figure 4 shows the different responses to abrasion at the end of the tests for filler contents of 0, 1 and 4 percent All plastic fillers except vent dust reduced abrasion. Vent dust caused an increase in the abrasion when only 1 percent was incorporated in the concrete, but it reduced the abrasion when the content was increased to 4 percent. 

VD-1 concrete suffered less scaling than the reference concrete. But the addition of vent dust beyond 1 percent increased the scaling to that of plain concrete when the level was 4 percent. 

It is clear from the results that of all the plastic fillers only the VD-1 concrete performed better than the control mix. It could be that the ability to absorb the stresses due to temperature changes was enhanced by the presence of a small amount of vent dust. 

The small size fillers like HDPEfme and VD caused a strength reduction which can be traced also to their surface area. Vent dust proved to be very harmful to concrete strength even with just 1 percent of content level. Two factors may interact to reduce the strength. One is the lack of bonding between the plastic particles and the concrete paste. The second factor is the increased surface area of the plastic particles. 

A proposed impact test using concrete cubes in the Los Angeles abrasion machine proved to be an effective way for testing the resistance of concrete subjected to repetitive low impact loading. Only HDPEfme improved the impact resistance of concrete. The impact resistance of concrete was not affected with the incorporation of PET and PS flakes. Vent dust reduced the impact resistance of the concrete samples for both content levels. 

To save material means and the areas of industrial premises rooms due to an opportunity of installation bubbling— the vortieal device in vent dust removal system. 

Bubbling—the vortical device is supposed to mount in vent dust removal systems with the purpose of economy of the areas of industrial premises, thus hydraulic resistance of system does not exceed 500 Pa, power inputs on clearing of gas in 3 times below, than in known devices. 

---