Cornerstones of Compression: The Burckhardt Labyrinth Compressor
By Norm Shade30 May 2023
Unique reciprocating compressor technology was first introduced by Sulzer in 1935
The growth of the liquefied natural gas (LNG) market has resulted in the increased application of labyrinth compressors in both stationary and marine installations. Vertical, inline reciprocating labyrinth compressors employ a unique technology between the piston and the cylinder wall and between the piston rod and the piston rod sealing gland. The labyrinth sealing effect is created by numerous tiny throttling points that resist leakage from high pressure to low pressure. At each throttling point, pressure energy is transformed into kinetic energy as a result of the flow restriction. The process continues at each throttling point and volume chamber combination along the piston wall and along the piston rod gland until the required reduction in pressure is attained. A small clearance volume is maintained between the adjoining surfaces and the limited amount of gas passing through the sealing system is recovered internally. This contactless sealing of the piston and piston rod is accomplished without the need for lubrication and without physical contact that would result in mechanical friction or wearing of sealing elements in the compressor cylinder area. This provides advantages for contamination-free compression of pure gases, and labyrinth compressors have generally exhibited longer time between overhauls than other types of reciprocating compressors.
However, labyrinth compressors are not new. Most are produced by Burckhardt Compression today, but they were actually introduced first by Sulzer for ammonia compression in a brewery in Zurich, Switzerland in 1935. After several years of cooperation, Sulzer acquired the Burckhardt Engineering Works in 1969. A few years later, the business was renamed Sulzer-Burckhardt AG. Prior to that time, both Sulzer and Burkhardt had long industrial heritages, Sulzer most notably in steam engines and diesel engines, and Burkhardt in reciprocating compressors.
Sulzer was started in 1834 by Johann Jakob Sulzer-Neuffert in Winterthur, Switzerland. With his two sons, Johann and Salomon, the company began producing cast iron. In 1841, the Sulzer brothers produced their first steam engine. Joined in 1851 by English design engineer Charles Brown, Sulzer developed groundbreaking new steam engines for decades. In 1898 it began cooperation with Rudolph Diesel, leading to the development of the first Sulzer diesel engine. As early as 1880, Sulzer also started building refrigeration machines, an endeavor that later led to its development of the labyrinth compressor for oil-free ammonia compression used in refrigeration cycles.
Franz Burckhardt started his company in 1844 in Basel, Switzerland, manufacturing machines for the textile industry. In 1856, the company began to produce steam engines, and by 1883, it had developed and sold its first reciprocating compressor, a dry-running single-stage machine that produced a pressure of 87 psig (6 bar). Continuing under Franz’ son, August, the Burckhardt company began to develop high-pressure compressors. In 1913, it delivered a 4350 psig (300 bar) ammonia synthesis compressor to BASF in Germany, a customer that had purchased one of Burckhardt’s early compressors back in 1885. In the 1920s, the company started developing compressors for 12,327 psig (850 bar) and then 14,500 psig (1000 bar) ammonia synthesis processes. By 1948, Burkhardt’s high-pressure technology had progressed to the production of a special 58,000 psig (4000 bar) compressor for a pilot plant in the U.S. and in 1951 it produced eleven 21,750 psig (1500 bar) hyper compressors for the production of polyethylene (LDPE).
Beginning in 2000, Sulzer began to divest several of its divisions to refocus its business. This was completed in 2002, when Sulzer-Burckhardt was sold to its management team, becoming Burckhardt Compression. In 2006, Burckhardt Compression emerged as a publicly traded company, and it was among the worldwide leaders in a wide range of reciprocating compressor technologies.
Originally designed in 1935 for the safe compression of ammonia, continuous improvements and further developments by Burckhardt have resulted in labyrinth compressors being used in thousands of installations for numerous applications handling complex gases. They have been used for decades for handling boil-off gas in LNG receiving and export terminals and other cryogenic applications. A few other specific examples of labyrinth compressor applications include compression of oxygen for steel production, carbon monoxide for acetic acid production, and polypropylene. Many others include compression of bone-dry gases; humid (wet) gases; dirty, dust-laden, contaminate gases in fouling services, clean gases where no contamination is allowed, and reactive, explosive, corrosive or toxic gases.
The non-contacting operation of the moving piston and piston rod requires precision lubricated guide bearings that keep the linear moving components from contacting the stationary compressor cylinder bore and piston rod gland. The vertical throw configuration, extra-long distance pieces and oil scrapers on the guide bearing keep oil from entering the process gas section of the compressor. Burckhardt’s labyrinth compressor line has evolved to a wide range of products involving two models capable of compressing gases to as much at 2200 psig (152 bar). The K-type is a gas-tight design with two to four throws with compressors ranging from 3.5 in (90 mm) stroke at 1000 rpm to 6.5 in. (165 mm) stroke at 750 rpm and power ratings from 154 hp (115 kW) to 2226 hp (1660 kW) or higher. The D-type design has two to six throws with compressors ranging from 5.5 in. (140 mm) stroke at 1000 rpm to 14.8 in. (375 mm) stroke at 380 rpm and power ratings from 233 hp (174 kW) to 5460 hp (4000 kW) or higher. Even higher pressures are possible with special sealing arrangements.