The global demand for alternative fuels continues to increase and diversify. Cement companies are under increased scrutiny to deliver high quality products in a safe environment, while continuing to increase their efficiencies. The need to reduce kiln operating fuel costs therefore remain one of the largest goals for cement producers. Traditionally this has involved solid wastes, particularly from municipal sources. Here, however, Ted T Reese of Cadence Environmental Energy highlights the potential to use wastes from the oil refining industry as alternative fuels for cement production.
Significant increases among a variety of alternative fuels have been achieved in many major markets including Europe, the Americas, Asia, and many other regions by a wide range of cement companies. Municipal waste and biomass materials continue to be at the forefront of many of these new developments. Cement manufacturers are specifically focused on these materials due to their large supply and potential for reducing fossil fuel use. There are, of course, many factors associated with taking these wastes and turning them into usable high-quality fuels, including numerous hurdles.
The solid shredded alternative fuel market garners most of the attention from waste generators and cement plants, as well as various vendors in the business of preparing, delivering and conveying alternative fuels. However, as the need for reducing fuel costs remains high, demand will not be met solely with these types of solid materials. It is, therefore, imperative to continue to search for additional wastes that can be used as alternative fuels. The petrochemical and refining industry is one source that has been underdeveloped and could offer high-quality alternative fuels in many markets.
Increased refinery investment and capacity
Saudi Aramco will invest US$90bn between 2012 and 2017 to increase its refining capacity by 50% up to 6 million barrels per day (mbpd). Most of this increase is being developed in Asia, primarily in China.1 The UAE has also announced it will increase its refining capacity to 1.1mbpd by 2017 from 707,000bpd at present.2 Meanwhile, Motiva, a joint venture between Saudi Aramco and Shell Oil, invested US$10bn to create the largest refinery operations in the United States. The refinery is located in Port Arthur, Texas and has a capacity of 600,000bpd. With all of these investments (and others) being made, refining capacities will continue to increase, as will the amount of waste they produce. Some of the wastes will be potential alternative fuels for the cement industry.
The refining process
Refining is the process of manufacturing petroleum products and other usable products from crude oil. There are many variations and types of crude oils from around the world. Selection is critical and influences the potential products and the cost of making them.
The first stage of crude processing is distillation, in which the crude oil is separated into varying components based on their boiling points. There are many processes used, including hydroprocessing, reforming and catalytic cracking. As well as producing many final products within the refinery, all of these processes remove impurities from the crude oil. In addition to the many processes there are also large quantities and volumes of stored hydrocarbons. The refineries, unlike the petrochemical and chemical industries, generate a small percentage of waste in comparison to volumes of products made. However, significant opportunities do exist for alternative fuels based on the very large crude oil volumes processed.
Identifying alternative fuel opportunities
As Cadence enters its 40th year in business, primarily as a North American fuel supplier, many lessons have been learned by developing successful alternative fuel programs. Three keys to a successful alternative fuel programme are:
1. Identifying a qualified and successful fuel supplier;
2. Identifying and securing a long term fuel supply;
3. Building a lasting relationship between the kiln, the fuel supplier and the fuel source.
Cadence is also entering its 30th year as the exclusive hazardous waste fuel supplier to Ash Grove Cement in the United States. Over 150,000t of liquid waste derived fuels (LWDF) are provided annually and used as alternative fuels at both of Ash Grove's fully permitted Resource Conservation and Recovery Act (RCRA) Part B Facilities. LWDF heat content ranges between 19 - 28MJ/kg. In addition to the liquid supply, Cadence has also supplied a variety of solid wastes (primarily hazardous materials) focusing on high revenue and high heat content fuels. These solids have been fed to the kilns from containers, sacks or in bulk. The combination of high revenue (disposal fees) in addition to high heat content materials is critical in selecting long term supply sources. Solid heat content ranges from 10 - 17.5 MJ/kg.
Using these historical fuel values as a basis for cement kiln alternative fuels, multiple opportunities have been identified in the refining process.
Fluid catalytic cracking slurry oils
The most profitable process in the refinery is the fluid catalytic cracking (FCC) unit where gas oils are 'cracked' to produce valuable gasoline and distillate fuels. Catalysts are used in this process and often carry over, which contaminates the slurry oil. Some slurry oils are sold as feedstock to other industries. However, a significant volume of this material accumulates and is stored in large tanks.
As the oil has already been processed, it has less value in the refinery than unprocessed crude oils and is often viewed as a waste. However, this waste is a valuable alternative fuel to the cement kiln, as its heat content can be as high as 21.3MJ/kg.
The slurry oil is often transported in vacuum boxes as it contains both free liquids and solids, giving a sludgy consistency. In addition the material also contains elevated levels of alumina and silica. This comes from the catalysts used in the FCC units and can sometimes be of value to cement kilns in cases where additional aluminium and/or silicon content is required in the feed.
Waste | FCC slurry oil |
Physical characteristics | Pourable sludge / Oil with free liquids |
MJ/kg | 9.3 - 21.3 |
% Chlorine | 0.1 - 0.8 |
% Water | 0 - 13% |
% Ash (Furnace) | 30 - 55% |
pH | 5 - 8 |
Mercury (ppm) | 0 - 1* |
SiO2 | 11 - 17% |
Al2O3 | 14 - 24% |
Fe2O3 | 0 - 6% |
Above - Table 1: Physical and chemical characteristics of FFC slurry oil.
* Mercury is a naturally occurring element varying in the crude oil. Content can be less than 1ppm with high levels seen at 5 - 10ppm.
Wastewater treatment (WWT) – Oil recovery
Crude oil contains contaminants known as basic sediment and water (BS&W). These exist in an emulsion form and generally account for 1 - 3% of the crude oil content. BS&W is removed from the crude oil prior to refinery processing. The material is sent to the wastewater treatment (WWT) area where the refiner's primary goal is to recover the valuable unprocessed oil. Three phase centrifuge operations are commonly used to separate the oil, water and solids. The refiner treats and releases the water, reprocesses the oil as a feed stock and disposes of the solids. Some refiners chose to send these solids (either in solid or emulsion form) internally to their coker unit as opposed to sending offsite for waste treatment. This is an option that is used but does have downside as it devalues the coke product. The centrifuged solid is the alternative fuel opportunity for the cement producer. These solids have heat content values between 8 - 16 MJ/kg and are often transported in roll-off boxes containing minimal or no free liquids.
Waste | WWT Centrifuged solids |
Description | Solid |
MJ/kg | 7.7 - 16.3 |
% Chlorine | 0 - 2 |
% Water | 20 - 50% |
% Ash (Furnace) | 20 - 35% |
pH | 7 - 9 |
Mercury (ppm) | 0 - 7 * |
SiO2 | 2 - 19% |
Al2O3 | 1 - 14% |
Fe2O3 | 1 - 8% |
Above - Table 6: Physical and chemical characteristics of WWT centrifuged solids.
* Mercury is a naturally occurring element varying in the crude oil. Content can be less than 1ppm with high levels seen at 5 - 10 ppm.
Conclusion
The opportunity to use increasing and diversified volumes of alternative fuels in the cement industry remains high. The oil refining industry offers several opportunities for waste materials to be used as such. However, as with all alternative fuels, identifying these materials and developing a long-term supply programme is critical to the success of the programme for the cement producer.
References
1. Oil & Gas News, February 2015.
2. Egypt Oil & Gas, 'Aramco to invest US$90bn in boosting refining capacity,' February 2012.