Elsevier

Powder Technology

Volume 112, Issue 3, 31 October 2000, Pages 229-234
Powder Technology

An investigation into the effect of product type when scaling for diameter in vertical pipelines

https://doi.org/10.1016/S0032-5910(00)00291-6Get rights and content

Abstract

The prediction of pressure drop is important to pipeline design and it is often necessary to use data from one pipeline size to predict what will happen in another pipeline size. This paper looks at the effect of two different products when scaling for diameter in vertical pipelines. Data has been measured for cement and flour in two bore sizes. A means of modelling has been established to allow prediction of the operation of a pipeline of one bore size, from trials on another bore size in vertical sections. The model used to correlate pipeline diameter with pressure gradient data in vertical pneumatic conveying pipelines will be discussed along with the general data trends for the two materials.

Introduction

The major design criteria for pneumatic conveying systems are those of pipeline bore, air mover rating, and solids feeder type. Each of these parameters is, in turn, determined to some extent by the system pipeline pressure drop. Thus, the importance of pressure drop prediction for pneumatic conveying pipelines will be self-evident. The investigations into the effect of pipeline diameter on the relationship between pressure gradient, solids flow rate and air flow rate in pneumatic conveying systems have mainly focused on pneumatic conveying in horizontal pipelines (e.g. [1], [2]). Although some work has been undertaken on vertical pipelines and the relationship to pressure drop in horizontal pipelines (e.g. [3], [4], [5]), the effect of bore size, although explored to a limited extent in vertical pipes (e.g. Ref. [6]), has not been exhaustively researched.

Many of the techniques, which have been presented for pipeline design in practical situations, rely on conveying trials in a pilot scale instrumented test facility [1]. Data obtained from the trials is then processed by empirically determined techniques to predict the likely pressure drop in the desired plant pipeline. Clearly, the availability of a suitable pilot scale test plant is key to such a design technique, and the cost of undertaking the pilot conveying trials can be significant. Therefore, it is usual to limit such trials to a minimum, on a pilot facility as small as can be used effectively, which means it is almost always necessary to scale for pipeline bore between trials and plant. This paper presents comparisons of pressure drop data measured from two vertical pipelines of different bore sizes. The details of the test facility along with the material employed for the test programme are presented. The approach used to analyse the data is presented, followed by a discussion on the processed data and the conclusions from this study.

Section snippets

Test facility

The test facility could be configured to enable tests to be carried out in either an 81-mm bore pipeline or a 53-mm bore pipeline. Both pipelines were of steel construction and a common layout was adopted to try to ensure that both pipelines were within less than 2 m of the same total length. Fig. 1 shows a schematic diagram of the test facility used to obtain data relating to both pipelines sections. The test material was conveyed from a top discharge blow tank, via the test pipeline section,

Test materials

Ordinary Portland Cement and wheat flour were selected for the test programme. To assess the effect of repeated conveying on the materials, the first five tests were repeated after every thirty test runs. It was found that the change in pressure gradient with repeated conveying was not significant compared to the size of the pressure gradient. The cement that was used for the tests was a standard grade cement readily available to the building and construction industry, having a mean particle

Experimental programme

Tests were carried out in the two vertical pipeline sections using the cement, and wheat flour approximately 250 test runs being performed in total. The range of superficial air velocities, from 5 to 23 m/s, was covered and this was consistent with both dense and lean phase conveying regimes. A suspension density range from 10 to 300 kg of cement per cubic metre of air was covered. However, due to both the limitation of the test plant and the requirement to make the test data applicable to the

Experimental results

The raw data from the tests in both the 81-mm-diameter pipeline and the 53-mm pipeline was initially analysed to give pipeline pressure profiles (as per the sample shown in Fig. 4) for each test run completed. Tangents were then fitted to the pressure profiles as indicated, in order to obtain the average pressure gradient along the pipeline straight, excluding any bend effects.

Values of pipeline pressure gradient were then tabulated for each test run completed, along with the relevant

Discussion

Fig. 6, Fig. 7, Fig. 8, Fig. 9 show the solids flow contribution to the total pressure gradients in the 81-mm bore pipeline and the 53-mm bore pipeline for both cement and flour. It is apparent from these that the solids contribution to the pressure drop is related linearly to the suspension density for any given air velocity, for both materials and pipeline sizes. This is, in itself, a useful result in terms of characterisation of the conveyability of materials in general.

However, what is more

Conclusions

Two bulk solids have been conveyed over a very wide range of flow regimes (from low-velocity, high-concentration dense phase flow to high-velocity, low-concentration lean phase flow) in two pipeline sizes, and the pressure gradients measured. From the results, a notional “solids transport contribution to pressure gradient” has been obtained by subtracting the pressure drop needed to transport the air and a notional gravitational “static head” contribution.

The conclusions of this study are that

References (7)

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