1. Evaluation principles of industrialized oil shale dry distillation furnace

(1) Advanced. It is mainly to examine the oil yield of an industrialized dry distillation furnace process on aluminum retort. It is usually considered that its oil yield to aluminum retort is as high as 85%, then its process is more advanced; and below 70%, it is not advanced enough. Of course, in addition to the oil yield is the key, there are other indicators to consider, for example, industrial-scale single furnace capacity is usually considered to be greater than 1,000t / d. In addition, the advanced nature should also include the thermal efficiency of the product, the low energy consumption of water, electricity, steam, and the high quality of the product (the quality of the shale oil, the calorific value of the distillate gas, etc.). Also important is the degree of environmental impact of the dry distillation process.

(2) Maturity. The main thing is to look at the annual start-up rate of industrialized dry distillation furnace, and its longest operating cycle. A mature industrialized furnace should have an annual start-up time of more than 7200h, that is, more than 10 months of operation. History has shown that the development of a completely new dry distillation process, from laboratory to small, to pilot, to semi-industrial, to large-scale industrialization, often takes not a few years, but a decade, or even decades, to succeed.

(3) adaptability. Dry distillation furnace process should be easy to operate, easy to regulate, can adapt to the performance of the raw material shale and processing capacity changes. Less pollution occurs during processing, should be easier to manage.

It should be suggested that the dry distillation process that can all meet the above three evaluation criteria is, of course, the most ideal.

2. Comparison of the main dry distillation processes in oil shale

Currently, there are six main processes in the world for the production of shale oil by dry distillation of oil shale (Table 3-1), namely, the Fushun-type furnace in China (block shale dry distillation furnace), the Petroseks furnace in Brazil (block shale dry distillation furnace), the Kivit furnace in Estonia (block shale dry distillation furnace), and the Groot furnace (granular shale dry distillation furnace), and the Grote furnace (particle shale dry distillation furnace), and the Grote furnace (block shale dry distillation furnace). Furnace (granular shale distillation furnace) in Estonia, and the Tasek Furnace (granular shale distillation furnace) in Australia. With the exception of the Tasek furnace, which is technologically immature and is currently out of industrial production, all other dry distillation furnaces are technologically mature and are relatively common in industrial production (Hou, 1984; Schmidt, 2002; Yefimov et al, 1982; Golubev, 2003; Schmidt, 2003).

In comparison, the Grote furnace is the best, followed by the Petrosex and Tasek furnaces, which are suitable for large and medium-sized oil shale refineries. And the improved Fushun type furnace in China is more suitable for small oil shale refineries.

Table 3-1 Comparison of current world oil shale dry distillation of major processes

Continued

3. Selection of oil shale dry distillation furnace

China's Fushun-type furnaces to deal with the small volume of oil yield is low relative to the laboratory aluminum retort, dealing with block shale, crushed shale can not be used, the shale utilization rate of only 80%, the process is not too advanced. Environmental performance is not good, but for the mature furnace, can deal with poor ore, good operating flexibility, there is a long-term operating experience and less investment, fast construction, suitable for small plants. Although the single furnace capacity is small, the Fushun type furnace can be combined with 20 units into one, *** with a set of condensation recovery system, the daily capacity of one furnace can be up to 2000t (Qian et al., 2006). Improved Fushun-type furnace can be 40 units into one (called "E part"), *** with a condensation recovery system, a furnace daily capacity of up to 4000t.

Estonian Vitro furnace processing capacity is larger, relative to the aluminum retort oil recovery is not too high, processing block shale, shale utilization rate of only 80%, is a Mature furnace, environmental performance is not good, medium investment, suitable for medium-sized plants.

Brazil's Petroseux furnace has a large capacity, handles block shale, has a high oil yield relative to aluminum retorts, produces high calorific value gas, is a mature furnace, has a better environmental performance, has a high investment, and is suitable for medium and large-sized plants (Qian et al., 2006).

The Estonian Grote furnace has a large processing capacity, can handle granular shale (can all use the original shale), the furnace relative to the aluminum retort has a high oil yield, produces high calorific value of the gas, is basically a mature type of furnace; wastewater is less, easy to deal with, is an environmentally friendly device; however, the structure is more complex, the maintenance cost is high. It is reported to run 7200h per year and can be used in large and medium-sized plants (Qian et al., 2006).

Australia's Tasek Furnace has a large capacity to handle granular shale (which can all utilize the original shale), with a high furnace oil yield and high calorific value gas. Shale oil after hydrogenation, good quality, high investment, but not yet very mature, only 60% of the operating rate before the shutdown in 2004, large and medium-sized plants can consider using this technology.

The choice of dry distillation furnace type must also be based on the nature of the oil shale used. In addition to emphasizing the bottom line of oil shale aluminum retort oil content, the dry distillation of oil shale dry distillation gas yield and the calorific value of the shale semi-coke, but also very important, because the calorific value of the dry distillation gas and semi-coke should be sufficient to provide the heat required for dry distillation of oil shale.

To adopt the dry distillation furnace type developed in Brazil, Estonia and so on, there are commercial aspects such as technology introduction, technology transfer or cooperative construction, and if the commercial negotiation is not successful, there needs to be an alternative.

Can use mature Chinese furnace type, for example: Fushun type furnace or gas-fired square furnace, although the oil yield is lower, but the investment is small, quick results. Can also use China's own research and development of the furnace type, such as: Dagong solid heat carrier dry distillation furnace or powder shale fluidization dry distillation furnace. However, it is important to know that both Dagong Xinfa dry distillation furnace type or fluidized dry distillation furnace type, is still in the pilot stage, to develop into an industrial-scale furnace, need to invest a lot of energy and risk investment, in the medium-sized and industrial-scale test success before the construction of industrial production units. Of course, for the sake of independent innovation and the development of new furnace types, such a choice is also worthwhile.

4. Condensation recovery system for oil shale dry distillation

The oil and gas exported from the dry distillation of oil shale is mainly in the gas phase, and condensation is required to recover shale oil and other products. The composition of the outlet gas from the furnace can vary greatly depending on the oil shale dry distillation process.

For block oil shale dry distillation furnace, the oil shale is heated by hot gas heat carriers for dry distillation, as mentioned earlier, Fushun generator furnace oil shale in the furnace is heated by hot recycling gas and hot gas to carry out the dry distillation. These two gases used for heating is a large number, more than the oil shale dry distillation of shale oil and gas to be more than ten times larger, therefore, dry distillation of shale oil and gas is generated by a large number of inert gas (nitrogen and carbon dioxide formed after the combustion of air) diluted, which makes the condensing system needs to a large number of the export of oil and gas to be cooled, and thus condensation and recovery system will be more large-scale equipment, and the condensation and recovery of the gas out after the recovery After condensation recovery, the calorific value of the gas is not high.

For the Brazilian Petrosexuals dry distillation furnace, the oil shale in the furnace is generated by the dry distillation of its own dry distillation gas heated by the formation of the thermal cycle of the gas to heat the dry distillation, this gas used to heat the heat carrier is also a large number of, more than the dry distillation of shale oil generated by the gas will be more than a dozen times larger, and therefore the condensation recovery system equipment will be relatively large. However, the calorific value of the dry distillate gas exiting the condensation recovery system unit is high due to the absence of inert gas (Rezende, 1982).

For pelletized oil shale solid heat carrier distillation furnaces, the oil shale is heated for dry distillation by a hot solid heat carrier (usually hot shale ash), such as the Groat and Tasek furnaces, and therefore, the furnace outlet oil gas is only the shale oil gas from the dry distillation of the oil shale itself, which is not large enough to require a small load on the condensation recovery system and a small unit. The calorific value of the dry distillate gas exiting the condensation recovery system unit is high. Due to the small load of the condensation recovery system, the water consumption is also small, and the sewage discharge is small, which can go to the boiler to be burned, which is good for the environmental protection, and it is a kind of environmentally friendly furnace type.

For powdered shale fluidized dry distillation furnace, oil shale, although it is heated by a hot solid heat carrier (usually hot shale ash) to heat the dry distillation, such as the Maoming two ware fluidized dry distillation device, but due to the fluidized agent into the dry distillation reactor, so out of the dry distillation reactor in addition to shale oil and gas in the gas, but also mixed with the fluidized agent, regardless of whether the fluidized agent used is superheated water vapor or distillation of the recycled gas, but also a large number of increase the load on the condensation recovery system, and the condensation recovery equipment is not small. But the distillate gas coming out of the condensation recovery system unit has a high calorific value.

There is also an important issue regarding the de-dusting of shale oil and gas. The dry distillation of oil shale, especially the dry distillation of granular shale and powder shale, the oil and gas exported from the dry distillation furnace will be entrained with a lot of dust, and when it enters into the condensation recovery system, the shale oil after condensation will contain a lot of dust, which greatly affects the quality of the shale oil, and even can't be used. What's more, the dust in the oil and gas, along with the condensation of shale oil, will lead to the blockage of dust in the condensation recovery system, thus affecting the normal operation of the whole dry distillation unit or even stopping the work. Therefore, particles, especially powder shale dry distillation furnace outlet of oil and gas, before and after entering the condensation recovery system, its dust removal problem is the first priority.

Oil shale dry distillation of different process units of the condensation recovery system comparison is shown in Table 3-2.

See from the above table, the different processes of dry distillation furnace outlet oil and gas first need to be dusted, for the dry distillation of massive shale, generally using water or oil washing, in addition to the next heavy oil entrained dust, and then settle and separate (Fushun-type furnaces and Kivette Furnace), or with the rotary splitter Remove the heavy oil with dust, and then filter separation (Petrosex furnace). For dry distillation of granular and powdered shale, due to the high amount of dust brought out, it is necessary to use two to three-stage cyclone separator to remove the dust.

Table 3-2 Comparison of condensate recovery systems for different process units for oil shale dry distillation