An Economic Analysis of Pipelining Beef Cattle Manure
Anaerobic digestion (AD) of manure can extract useful energy in the form of a medium heating value gas. AD has been implemented on a variety of scales, from small farm-based units to centralized digesters processing manure from multiple sources. AD has significant economies of scale, i.e., per unit processing costs decrease with increasing size. Some regions have a very high concentration of beef cattle in feedlots. For example, near Lethbridge, Alberta, more than a million beef cattle are in feedlots at any point in time; the comparable figure for Dodge City, Kansas, is more than two million. As part of a larger study of the economics of centralized manure processing, we have developed an economic model for the pipelining of beef cattle manure to a centralized AD plant and digestate from the plant back to the manure source for spreading. The model combines rheological and fluid mechanical properties for manure slurry with design and economic data for a pipeline and pumping stations. The model calculates an overall transportation cost for slurried manure that includes capital recovery. Unlike trucking, pipeline transportation of manure has a strong scale dependency; the unit transport cost decreases with increasing capacity. Manure pipelining costs are minimized when transporting manure at 12% to 14% slurry solids concentration in the pipeline. Two-way pipelines carrying manure to and digestate from the plant require less capital investment and operating costs relative to two separate manure and digestate pipelines.