Black powder

Introduction
Black powder is a general term used to describe a host of corrosion related contaminants that are very commonly found in pipelines that transport natural gas, hydrocarbon condensate and LPG. Black powder is made of very fine particles whose size is mainly in the 1-10 micron range. Despite its size, black powder is detrimental to pipeline equipment. It can also be easily transported to the end-user plant or to the receiving terminal where it can be the cause of numerous operation and maintenance issues.

Different types of separation technologies exist to remove solid contaminants from pipelines, but their efficiency can be inadequate. The installation of a high-performance, properly designed filter is an efficient and cost-effective solution to enhance the reliability of pipeline operation.

Case Study
A Middle East petrochemical company is receiving natural gas from the gas grid. Supply is 95 MMSCFD at an operating pressure of 425 psig. The plant uses the gas for various purposes: as a process gas and it must be compressed prior to further processing, and as a fuel gas to feed a gas turbine and burners.

Prior to entering this equipment, the total natural gas flow was passing through a knock-out drum equipped with a demister pad to remove liquids, then through filters to remove solid contaminants. Each filter vessel was equipped with 27 filter cartridges with a 4˝ diameter. These were cylindrical surface type filter cartridges, with a removal rating of 10 microns nominal as per supplier data.

Since 2003 the plant had been reporting several operational and maintenance issues, mainly on the compressor, which were causing recurrent maintenance activities due to cleaning and repair. 

Eventually these issues appeared to be related to black powder contamination transported with the feed gas. The plant reported that the impeller of the compressor had broken once during operation, which had caused damages on the casing and other internal parts. The plant also reported that control valves were blocking, and heavy black deposits were found in the compressor. In the inlet knock-out drum, significant quantities of black materials were collected (2000 kg in 2003 and 1600 kg in 2004), and the demister pad appeared to be severely damaged. Finally, filters were fouling very frequently, on average every two weeks. Analyses of deposits revealed that contamination was mainly made of iron sulphide particles.

The plant concluded that existing nominal rated 10 micron filters were not efficient enough to remove black powder properly. In 2006 the plant entered into discussions with filter suppliers to help them solve contamination issues of the feed gas. The plant initially wanted to retrofit the existing 10 micron filter with 1 micron rated cartridges, and to install a new 5 micron rated filter upstream as a pre-filtration stage. In order to minimize the investment cost, and to optimize the filtration sequence, the plant finally considered a single stage filtration system equipped with 1 micron absolute-rated Pall® Coreless filter cartridges with a depth, graded pore structure, polypropylene made filter media. A filter vessel was supplied, equipped with 30 Pall Coreless filter cartridges. During the sizing process, attention was given to the flow distribution around the filter elements in order to get favourable conditions for the formation of a filter ‘cake’ around each cartridge, thus increasing the solids removal capacity of the filter and its service life.

Filters were put on stream at the end of 2006. The dirty filters were replaced in mid-2008 after 20 months of successful operation, with no maintenance requirement on the downstream compressor. In 2007, after six months of operation, performance tests were run at the request of the plant, in order to measure the solids content upstream and downstream of the filter. Tests confirmed the good performance of the filter, with an outlet solids content of <0.01 ppmw, while the inlet solids content was 0.61 ppmw at the time of testing. At the opening of the filter vessel in 2008, the filter elements were in very good condition. The Black Powder appeared to be dry. As expected the finest particles had been trapped within the depth of the filter media, while the dry black powder had formed a 3-10 mm thick ‘cake’ on the outer circumference along the cartridges, which represented an additional dirt removal capacity to the filter elements.

The modification of the filtration stage with a properly designed technology has enabled the plant to reduce its annual maintenance costs through a more efficient protection of the compressor, as well as its operating costs due to less frequent filter replacements. The average filtration cost with the new filter technology is less than $10 / 100 MMSCFD, representing a reduction of about 10 times of their previous filtration costs.

Conclusion
Black powder particles are present as very fine particles, typically in the micron range. Although they are very fine, they are also very detrimental to the pipeline components and to the machinery and equipment at the end-user’s plants. These fine particles are difficult to remove efficiently. Filters with a poor construction, a poor sealing, or with a nominal rating are not appropriate for this application.

Pall Coreless filters are perfectly suited for gas filtration. Thanks to its depth, graded pore construction it can remove very fine particles while providing a long service life.

Figure 1: Pall® Coreless 1 µm absolute rated pore depth filters after successful run of 20 months

About Pall Corporation:
Pall Corporation (NYSE:PLL) is a filtration, separation and purification leader providing Total Fluid ManagementSM solutions to meet the critical needs of customers in biopharmaceutical, hospital and transfusion medicine, energy and alternative energy, electronics, municipal and industrial water, aerospace, transportation and broad industrial markets. Together with our customers, we foster health, safety and environmentally responsible technologies. The Company’s products enable process and product innovation and minimize emissions and waste. Pall Corporation is an S&P 500 company with more than 10,000 employees servicing customers worldwide. To see how Pall is helping enable a greener and more sustainable future visit www.pall.com.

Global company – Local presence
From regional offices in Dubai, Pall provides support and sales to the Middle East oil and gas production and processing companies, including GCC countries and Egypt. Pall’s presence has strengthened in the MENA region from two engineers in 2004 to 35 in 2008 plus sales, marketing, and laboratory services, test rigs, pilot and demonstration plants, demonstrating a commitment to provide world class filtration and separation solutions to the region by being close to its customers.