Hydrotransport 15 Conference Prediction of pump discharge pressure for Rugby Cement 92-km chalk slurry pipeline N J Alderman, N I Heywood, Hyprotech UK Ltd, UK D J Clowes, Rugby Cement, UK Hydrotransport 15 Conference 3 to 5 June 2002, Banff, Canada © 2002 AEA Technology OHT serial no 1 1

Rugby Cement Chalk Slurry Pipeline Pipeline in operation since 1964 Supplies chalk slurry from chalk deposits in Kensworth, near Dunstable, Bedfordshire to Rugby Cement Works in Warwickshire 92-km long pipeline Consists (in 1999) of nominal 10 inch ID steel pipe Laid approximately one metre below ground level

Background to Study 1988: 1998: 1999: Owing to progressive corrosion problems arising from past pigging activities and presence of dissolved air, first 8-km from Kensworth was replaced with nominal 10 inch bore pipe. A further 16-km of pipe was replaced with nominal 10 inch bore pipe. Major pipe bursts occurred in old pipe along the 38-km intermediate section. On instruction from HSE in UK and to reduce potential for further pipe bursts, maximum discharge pressure from pumps at Kensworth was lowered from 109.1 bar to 88 bar.

Background to Study 1999: Agreed with HSE that 38-km section was to be replaced so that the capping of discharge pressure at 88 bar could be lifted. Proposed that this section be replaced with nominal 11-inch bore pipe. The 29-km northern section also needed to be replaced. Three options for this section: Nominal 10, 11 or 12-inch bore pipe. Systematic study of these options based on rheological testwork on chalk slurry samples at Kensworth Quarry.

Slurry Characterisation Particle Size Distribution pH Viscometric Tests Co-axial cylinder viscometer Bingham plastic model used, with yield stress and plastic viscosity correlated with moisture content

Chalk slurry particle size distribution

Flow curves for chalk slurries ranging from 29. 5% to 37 Flow curves for chalk slurries ranging from 29.5% to 37.2% moisture content

Bingham plastic model 6

Frictional pressure loss calculation for existing pipeline derived from Rugby Cement operational data where Pd = pump discharge pressure Pr = discharge pressure at pipeline exit which was taken to be atmospheric (1 bar absolute) = frictional pressure loss from flow through straight sections of pipework Pff = frictional pressure loss from flow through various types of fittings Ps = pressure loss or gain resulting from elevation changes

Frictional pressure loss calculation for existing pipeline based on Bingham plastic model fit to viscometric data Calculate Bingham Reynolds Number, ReB and Hedstrom Number, He Calculate friction factor, f and frictional pressure gradient, Pf/L

Pf/L data for chalk slurry with 36% moisture content as a function of pipe diameter (Q = 187 m3/hr)

Comparison of two methods of calculating Pf For chalk slurry of 36% moisture in existing pipeline at 109.1 bar = 126.7 bar Pf = 105.8 bar Difference between two values due to solids deposition in pipeline As thickness of any deposit formation in pipeline not known, use lumped parameter approach Assume difference between two estimates is due to reduction in flow area caused by deposition in pipeline Four pipe diameters 248, 254, 279 and 305 mm adjusted downwards by a multiplier until two estimates are equal Assume this multiplier (= 0.963), is applicable for other slurry moisture contents

Replacement of the middle 38-km, 10 in NB old pipe with 11 in NB new pipe New pipeline as agreed with the HSE made up of four sections: L1 = 8 km of 254mm ID pipe L2 = 16 km of 248mm ID pipe L3 = 38 km of 279mm ID pipe L4 = 30 km of 254mm ID pipe Pf for the total pipeline estimated from

Pf vs L plot showing comparison between existing 1999 pipeline and pipeline whose middle 38-km 10-inch NB pipe was to be replaced with 11-inch in NB pipe

Replacement of the final 30-km, 10-inch NB old pipe with 10/11/12-inch NB new pipe New pipeline made up of four sections: L1 = 8 km of 254mm ID pipe L2 = 16 km of 248mm ID pipe L3 = 38 km of 279mm (11-inch NB) ID pipe L4 = 30 km of 254mm (10-inch NB) ID pipe 30 km of 279mm (11-inch NB) ID pipe 30 km of 305mm (12-inch NB) ID pipe

Pf vs L plot showing three pipe diameter options for final 30-km section ( : 254 mm,  : 279 mm and X : 305 mm)

Pump discharge pressure as a function of moisture content for four different pipe scenarios

Pump power as a function of moisture content for four different pipeline scenarios

Specific energy requirement as a function of moisture content for four different pipeline scenarios

Conclusions (1) Comparison between measured and estimated frictional pressure losses for existing 1999 pipeline showed difference of some 20 bar, attributed to deposition of coarse particles on bottom of horizontal pipeline, although pipe wall roughness may also be a factor. Assumed that same percentage uniform reduction in pipe hydraulic diameter occurred for different pipe diameters comprising pipeline. Percent reduction was estimated by adjustment until estimated frictional pressure loss across pipeline matched predicted frictional pressure loss using operational data. Percent reduction of 3.7% used to predict frictional pressure loss, and hence pump discharge pressure requirements, for several combinations of chalk slurry moisture content and alternative pipe diameters for the final 68-km portion of pipeline.

Conclusions (2) As expected, predictions of pump discharge pressure increase with decreasing slurry moisture content, but the pumping power requirement and the SEC are largely insensitive to chalk slurry moisture content over 32% to 36% by weight. Suggests no saving in pump energy by reducing moisture content from 36% down to 32%. However, thermal energy costs at the cement works can be reduced by reducing slurry moisture content.