Design and Operating Characteristics Of the Sunflower Helium Plant
Authors: Crawford D.B. , Harlan J.D. 
Published: December 2007

The plant described here is designed to process feed gas having a broad range of compositions. Tolerating a wide seasonal flow demand, the plant produces crude helium, recovers 80 percent of C3+, and rejects nitrogen to produces crude helium, recovers 80 percent of C3+, and rejects nitrogen to maintain tail gas at a constant heating value.

Introduction

The Sunflower Helium Plant, located at Scott City, Kans., is jointly owned by Helium Inc., a subsidiary of the Kansas-Nebraska Natural Gas Co., and by Cities Service Cryogenics, Inc., a subsidiary of Cities Service Co. Each subsidiary owns a 50 percent undivided interest in the plant. The plant was designed, engineered and constructed by the M. W. Kellogg Co. and began operation in Sept., 1968. The Sunflower Helium Plant has been designed to accept a wide range of feed compositions, pressures, flow rates and ambient temperature conditions; as a result, it is one of the most versatile helium plants ever put into operation. Variations in feed conditions inherently produce a series of interactions of operating variables. To cope with both the feed variations and the operating interactions the plant has been designed to give the operator a wide selection in mode of operation and control. The plant can process as little as 110 MMscf/D of natural gas in the spring and fall, and as much as 200 MMscf/D in the winter. This wide range in processing capability is for the purpose of optimizing the annual yield of products and return on investment. The plant has been designed to produce crude helium (80-percent purity), pure (99.5 percent) nitrogen, and tail gas purity), pure (99.5 percent) nitrogen, and tail gas (945 Btu/cu ft) and to recover 80 percent of the C3+. At this point let us consider the fact that the helium concentration in the plant feed is only about 0.5 mol percent. As a result, most of the equipment (with the percent. As a result, most of the equipment (with the attendant operating problems) in a helium plant is concerned with the handling of the bulk natural gas; and the part of the plant where helium finally appears as a major component is a relatively small section.

Basis of Design

Basically, the Sunflower Helium Plant consists of two natural gas liquids recovery plants operating in parallel. Only one plant produces helium and we shall parallel. Only one plant produces helium and we shall continue to refer to it as the helium plant. It is designed to process 75 MMscf/D of feed gas at a constant daily rate throughout the year. In parallel with the helium plant is a cryogenic natural gas liquids (NGL) plant is a cryogenic natural gas liquids (NGL) recovery plant that is designed to process 93 MMscf/D; however, it processes as little as 35 MMscf/D in spring and fall and as much as 125 MMscf/D in the winter. When the flow exceeds 93 MMscf/D the liquids recovery percentage suffers. To illustrate the problem of varying load, Fig. 1 shows the nominal flow rate through the facility during the various months of the year. One line shows the helium plant operating at 75 MMscf/D and another shows it as 168 MMscf/D. The latter line represents the design basis for propane and ethylene refrigeration capability installed in the plant. It is evident that the design for 168 MMscf/D is inadequate to cope with winter loads and maintain maximum recovery of hydrocarbons. In the spring and fall when the load is relatively light, there is excess propane and ethylene refrigeration capacity. Note that there is an increase in gas demand in the hot summer months; this is because of air conditioning and farm product drying requirements.

JPT

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