Calculation of the Heat and Material Balance for Myanmar Oil Shale

Jul 8, 2016 - State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, ... E-mail: [email protected]. ... 2017 31 (2), pp 1...
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Calculation of the Heat and Material Balance for Myanmar Oil Shale Processing by Sanjiang Gas Combustion Rectangular Retort Jili Hou,† Shuyuan Li,*,† Yue Ma,† Cengceng Geng,† Lu He,† Yukai Zhu,† and Lei Zhang‡ †

State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, Beijing 102249, People’s Republic of China Shandong Energy Longkou Mining Group Company, Limited, Longkou, Shandong 265700, People’s Republic of China

‡

ABSTRACT: In this paper, with 1000 kg of oil shale for research, the heat and material balance of Myanmar oil shale processing by Sanjiang gas combustion rectangular retort (SJ-retort) was calculated. The results show that the heat requirement of Myanmar oil shale retorting can be satisfied by its high-calorie retorting gas combustion as well as the heat release from the retorting process. In the study, 33.26% surplus retorting gas is obtained, which indicates that the Myanmar oil shale processing by SJ-retort is theoretically feasible. In addition, a concise and accurate method is proposed to calculate the gas balance of the retorting process, which can calculate the dynamic equilibrium value of various types of gases (total input and output gases, recycle gases, and the new air that enters the retort) when the retorting system reaches a steady state. This method was validated with the successful operation of a pilot-scale test for oil shale retorting in Shenmu of Shanxi province and Yaojie of Gansu province in China.

1. INTRODUCTION Oil shale is a kerogen-rich fine-grained sedimentary rock, and its abundant reserves are the second largest among all fossil fuels in the world if converted into heat.1,2 Developing effective and economical methods to use oil shale has attracted increasing attention worldwide.3,4 A heat and material balance calculation is necessary to optimize the operating conditions, improve the efficiency, and reduce the consumption in the process of oil shale retorting. Some studies about heat and material balance have been conducted over the past few years. For lump oil shale retorts, Yefimov and Volkov5 used 1000 kg of oil shale for research and measured the input and output materials of the Kiviter retort; the result shows that the inputs and outputs were approximately 1450 kg, which is below the Sanjiang gas combustion rectangular retort (SJ-retort) value (1854 kg). Martignoni and Rodrigues6 studied the energy efficiency of the Petrosix retort; the results show that the energy efficiency was approximately 60%, which is below that of SJ-retort, with a 65% energy efficiency, because the Petrosix retort did not use the latent heat of semi-coke. Barnet,7 Baughman,8 and Nowacki9 studied the material yield and heat efficiency of Green River lump oil shale, which was processed using Unocal Union B retort and SGR-3 retort. They found that the energy efficiencies of the two retorts were approximately 70 and 83%, respectively, and that the heat value of retorting gas was 30 MJ/m3, which is close to that of the Myanmar oil shale retorting gas and can provide a greater quantity of heat for retorting. John and Joseph10 and Baughman11 studied the material and heat balance of Colorado shale of the Paraho retort for its two retorting processes (direct heated and indirect heated). Their results show that the weight percent of off-gas plus oil was higher from the direct heated process (93.0%) than that from the indirect heat process (77.5%) and the energy efficiencies were 89 and 75%, respectively, which are higher than that of SJ-retort. For particulate oil shale retorts, Golubev and Golmshtok12,13 © 2016 American Chemical Society

calculated the energy efficiency of UTT3000, which is 73− 88% and higher than that of SJ-retort. The produced retorting gas had a high calorific value (33.99 MJ/kg), which was higher than that of SJ-retort. Considering the green river oil shale, Brandt14 compared the energy consumptions of the Shell in situ conversion process (ICP) and Alberta Taciuk processor (ATP) technologies. The result shows that ICP (0.44−0.73 MJ/MJ) is more energy-intensive than ATP (0.40−0.52 MJ/MJ), even at a given scale (e- use). Most previous works focused on the study of material balance, and most data were obtained using simple field tests. Hence, there is no detailed analysis of the heat and material variation of each component, and there are notably few studies on the gas cycle balance of the retorting process. This paper theoretically deduces the heat and material balance of Myanmar oil shale processing by SJ-retort using the basic properties of oil shale and its pyrolysates. A concise and accurate method to calculate the gas balance of an oil shale retort is presented, which can preliminarily predict whether the retort can process the oil shale. In addition, this paper also provides a detailed introduction on the process structure of SJ-retort and compares it to other oil shale retorts.

2. DESCRIPTION OF SJ-RETORT 2.1. Simplified Structure of SJ-Retort. Figure 1 shows the simplified structure of SJ gas combustion rectangular retort. SJ-retort is an internal heating retort that supplies retorting heat by fuel gas combustion. It consists of a drying and preheating section, a pyrolysis section, a gas combustion section, and a cooling section.15 (1) Oil shale of lump size of 8−60 mm enters the retort from a feeder at the top and undergoes drying and preheating by its own weight. The gas-gathering cone and steel Received: May 16, 2016 Revised: June 30, 2016 Published: July 8, 2016 6373

DOI: 10.1021/acs.energyfuels.6b01178 Energy Fuels 2016, 30, 6373−6380

Article

Energy & Fuels

Figure 1. Simplified structure of SJ gas combustion rectangular retort.

structure are set at the top of the retort (1.1 m). First, the oil shale is uniformly distributed into the retort. Second, the rising gas is collected to make the retort ventilation uniform, which can make the temperature distribution more uniform and easier to control. (2) In the pyrolysis section, there is a large cavity in the furnace that helps to increase the furnace cross-area and effective volume, prolong the pyrolysis time, improve the yield of semi-coke and shale oil, regulate the heating gas volume to guarantee that the pyrolysis process runs more than 4 h at 550 °C, and ensure a maximum yield of shale oil at a low temperature.15 (3) In the gas combustion section, we used a venturi mixer and a grid wall to supply heat. The air and fuel gas that enter are mixed in the venturi mixer, and the generated hot combustion gas spurts into the grid wall. The air flows through the grid wall at a high speed and spurts from the flat hole of the crater brick. A total of 10 heating lines are on the large cross-section, and each line has 22 heating spots; thus, in total, there are 220 heating spots to uniformly achieve a maximum thermal energy. The high-speed airflow enters through the spurt hole of the grid wall with a high temperature to ensure that there is no hanging slag. 2.2. Comparison of Oil Shale Retorting Technologies. According to the comparison of oil shale retorting technologies described in Table 1, SJ-retort is widely adaptable because it can process bituminous coal, lignite coal, and oil shale. In comparison to other types of retorts in China, the SJ-retort produces a higher oil yield and heat efficiency. The single retort oil yield can be 85−86% versus the Fisher assay. With the processing capacity of 500 t/day for oil shale, the processing capacity can be further enlarged. In addition, other advantages of this type of retort are that it has a simple structure, has fewer capital costs, is easy to operate, has a short construction period, has stable operation, and has high economic benefits. The SJretort is suitable for small and medium oil shale retorting plants in China.

The SJ-retort also has some disadvantages: it is limited to lump oil shale; that is, the particle size of oil shale should be larger than 8 mm. In comparison to the particulate oil shale retort (Galoter and ATP), the SJ-retort has a lower yield and its processing capacity is lower than that of the Kiviter, Petrosix, SGR-3, and particulate and pulverized retorts. In addition, the low-oil-content shale cannot be processed by SJ-retort because its low-calorific gas cannot provide the heat needed for retorting.

3. EXPERIMENTAL SECTION 3.1. Materials. The typical oil shale used in this study was obtained from Mepale basin of Karen State of Myanmar. The raw oil shale was crushed and screened to 0−3 mm sized particles before use. The results of the Fischer assay and proximate analysis are provided in Table 2. The Fisher assay and proximate analysis were performed according to the ASTM standards (ASTM D3904-90 and ASTM D3172-13). 3.2. Retorting Gas Collecting and Composition Analysis. After the pyrolysis of oil shale in the Fisher assay, the pyrolysates (shale oil, water vapor, and retorting gas) passed through the outlet tube into a conical flask that was cooled in an ice−water mixture (0 °C). The condensable fraction remained in the conical flask. The remaining retorting gas was collected using a vacuum gas bag, and the composition was analyzed with an Agilent-6890 gas chromatographer. The chromatographic condition was as follows: an initial column temperature of 50 °C for 3 min, 5 °C/min to 100 °C for 0 min, and 10 °C/min to 180 °C for 3 min. The H2, air, and makeup (N2) flow rates of the flame ionization detector (FID) were 40, 650, and 20 mL/min. The front inlet pressure was 9.7 psi. The inlet pressure was 14.8 psi. Both temperatures of the injection port and detector of the FID and thermal conductivity detector (TCD) were 50 and 250 °C. The heat value and average molecular weight of retorting gas can be calculated according to the gas composition shown in Table 3. With high CH4, H2, C2H2, and CO contents, the heat value of the retorting gas was relatively high (30.79 MJ/m3) and the retorting gas was able to supply a greater heat requirement for oil shale retorting. 6374

DOI: 10.1021/acs.energyfuels.6b01178 Energy Fuels 2016, 30, 6373−6380

maturity

oil yield (%) (versus Fischer assay) energy efficiency (%) products

heat carrier heat source

country location company capacity (t/day) oil shale size (mm) type process

retort type

40 fuel oil, low-calorific gas, shale ash quite mature

shale char sensible heat 85−86

70 fuel oil, chemicals, high-calorific gas, shale char mature

China Fushun

Fushun retort

17

72−75 fuel oil, chemicals, low-calorific gas, shale char quite mature

shale char sensible heat 75−80

Estonia Kohtla Yarve VKG 200/1000 10−125 vertical cylindrical oil shale pyrolysis shale char cooling low-calorific gas retort gas latent heat

Kiviter retort

18

lump oil shale retorts (gas heat carrier)

100/150 10−75 vertical cylindrical oil shale pyrolysis shale char gasification low-calorific gas retort gas and shale char latent heat 65−70

China Yaojie YJ Coal and Electricity 500 8−60 vertical rectangular oil shale pyrolysis shale char cooling high-calorific gas retort gas latent heat

SJ-retort

16

Table 1. Comparison of the Industrialized Oil Shale Retorting Technologies

60 fuel oil, light oil, sulfur, high-calorific gas, shale char quite mature

shale char sensible heat 85−90

Brazil Sao Mateus Petrobras 1500/6000 6−50 vertical cylindrical oil shale pyrolysis shale char cooling high-calorific gas retort gas latent heat

Petrosix retort

19

73−88 fuel oil, chemicals, high-calorific gas, shale ash mature/test run

latent heat 85−90

Estonia Narva Narva Power 3000 0−25 horizontal cylindrical oil shale pyrolysis shale char combustion shale ash shale char

Galoter retort3,4,20,21

light fuel oil, low-sulfur light oil, high-calorific gas, shale ash prematuration

latent heat 85−90

Australia Stuart/Fushun SPP/CPM/Fushun 6000 0−16 horizontal cylindrical oil shale pyrolysis shale char combustion shale ash shale char

Taciuk retort22

particulate oil shale retorts (solid heat carrier)

Energy & Fuels Article

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Energy & Fuels Table 2. Fischer Assay and Proximate Analysis of Oil Shale (Received Basis) Fischer assay (%)

proximate analysis (%)

sample

oil content

water

semi coke

retorting gas

moisture

volatile

ash

fixed carbon

heat value (kJ/kg)

Myanmar oil shale

5.66

3.56

88.02

2.76

1.42

15.13

81.77

1.68

4132

Table 3. Main Compositions of Myanmar Oil Shale Retorting Gas composition

CH4

C2H6

C2H4

C3H8

C3H6

C4H10

C4H8

C5H12

C5H10

H2

CO2

CO

H2S

V (%)

17.22

6.94

2.30

3.15

3.22

1.41

2.75

0.55

0.36

28.27

26.05

5.95

1.84

4. RESULTS AND DISCUSSION 4.1. Heat Balance Calculation. 4.1.1. Heat Required for Myanmar Oil Shale Retorting. The required heat for oil shale retorting includes the heat needed to increase the temperature from room temperature (20 °C) to the pyrolysis temperature (550 °C) and the heat needed for pyrolysis, which is the sum of the sensible heat and pyrolysis heat. The sensible heat was calculated from the average specific heat in different periods of temperature increase. Formerly, the pyrolysis heat was estimated from retorting practice; currently, it can be determined using differential scanning calorimetry (DSC) (Table 4).23,24

The results are shown in Table 5. Table 5. Heat Required and Heat Provided for Myanmar Oil Shale Retorting heat required

MJ

heat provided

MJ

Q1 ΔQ* Q2 Q3 Q4 Qloss Qtr

4.75 32.05 12.91 288.45 545.98 176.83 1060.97

Q5 Q6 Q7 Q8

423.11 29.41 33.08 65.30

Qtp

550.90

Table 4. Physical Property Parameters 4.1.2. Heat Provided from the Retorting Process. First, 550 °C shale oil vapor, water vapor, and retorting gas can be obtained from oil shale retorting.25 When these components rise to the top and discharge from the retort, they exchange heat with the falling oil shale from the top of the retort and the temperature decreases to approximately 90 °C at the retort exit. Because of the supersaturated steam and negative pressure at the exit, the water will not condense into the retort. In addition, semi-coke is discharged from the bottom of the retort, and the exit temperature is approximately 90 °C after water cooling. Hence, the pyrolysates leave their sensible heat of 550−90 °C [sensible heat of semi-coke (Q5), sensible heat of retorting gas (Q6), sensible heat of water vapor (Q7), and sensible heat of shale oil (Q8)] in the retort as part of the heat supply for oil shale retorting. The total provided heat in the retorting process is denoted by Qtp. The result in Table 5 is obtained according to the formula Q = cmΔT. 4.1.3. Required Heat Complement. Because the provided heat from the retorting process cannot satisfy the heat demand for Myanmar oil shale retorting, retorting gas combustion must be used to provide the remaining heat as

physical property parameters pyrolysis heat required (dry basis) (kJ/kg) specific heat capacity of water (kJ kg−1 °C−1) specific heat capacity of water vapor of 90 °C (kJ kg−1 °C−1) specific heat capacity of water vapor of 550 °C (kJ kg−1 °C−1) specific heat capacity of water vapor of 90−550 °C (kJ kg−1 °C−1) specific heat capacity of oil shale and semi-coke (kJ kg−1 °C−1) specific heat capacity of oil vapor (kJ kg−1 °C−1) heat value of retorting gas (MJ/m3) specific heat capacity of retorting gas of 90 °C (kJ m−3 °C−1) specific heat capacity of retorting gas of 550 °C (kJ m−3 °C−1) specific heat capacity of retorting gas of 90−550 °C (kJ m−3 °C−1) gasification latent heat of water (kJ/kg) average molecular weight of retorting gas (g/mol)

293 4.19 1.88 2.15 2.02 1.05 2.51 30.79 1.80 2.84 2.32 2260 24.91

The moisture in the oil shale (received basis) experiences the following steps during the retorting process. Liquid moisture is heated from room temperature (20 °C) to 100 °C; the quantity of heat absorption is sensible heat (Q1). After the phase transition, the 100 °C liquid moisture changes to 100 °C water vapor; the quantity of heat absorption is ΔQ*, which is known as the latent heat of vaporization. Finally, the water vapor is heated from 100 to 550 °C; the quantity of heat absorption is sensible heat (Q2). In addition, for oil shale (dry basis, minus the surface water above), the retorting decalescence is (Q3) and the quantity of heat absorption need to heat from 20 to 550 °C is sensible heat (Q4). There is a certain quantity of heat loss during the retorting process, which is denoted by Qloss. During the whole retorting process, the total heat required Qtr is the sum of the above heat quantities. A total of 1000 kg of oil shale and 20 °C were chosen for the calculation basis, according to the formula Q = cmΔT + ΔQ *

(2)

Q complement = Q tr − Q tp

(3)

Vneeded = Q complement /Q ′heat value of retorting gas

(4)

PV = mRT /M

(5)

m = PVM /RT = 22.4V /M

(6)

where P is the pressure of ideal gas (atm), R is the ideal gas constant (8.314 J K−1 mol−1), and T is the temperature of ideal gas (K). Thus, the calculated complement heat (Qcomplement) is 510.07 MJ, and the volume of the required pure retorting gas (Vneeded) is 16.57 m3. According to the ideal gas state equation, the quality of required retorting gas is 18.42 kg.

(1) −1

Q tp < Q tr

−1

where c is the specific heat capacity (kJ kg °C ), ΔT is the temperature variation (°C), and ΔQ* is the latent heat of vaporization (kJ). 6376

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Energy & Fuels 4.1.4. Heat Balance of SJ-Retort. According to the result of Table 6, when the retort achieves a stable operation, the total

must be released for boiler combustion or other purposes after desulfurization. Finally, the input gases, recycle gases, and release gases achieve a dynamic balance. (3) Suppose that the pure retorting gas, which is produced by oil shale pyrolysis, was independent from other gases, such as N2, CO2, and SO2. (4) Suppose that the O2 and N2 contents of the atmosphere are 21 and 79%, respectively, and ignore the other gas components. The molecular formula of the retorting gas can be simplified as C1.0800H2.7076O0.5805S0.0184 according to the composition of retorting gas and its reaction equation with oxygen as follows:

Table 6. Heat Balance of SJ-Retort for Myanmar Oil Shale Processing (1000 kg, Received Basis) requirement (1) heat requirement for retorting oil shale (2) heat loss (20%)

total

MJ 884.14 176.83

1060.97

supply (1) sensible heat semicoke (2) sensible heat retorting gas (3) sensible heat water vapor (4) sensible heat shale oil (5) provided by recycle gas total

MJ of

423.11

of

29.41

of

33.08

of

65.30

C1.0800H 2.7076O0.5805S0.0184 + 1.4850O2 = 1.0800CO2 + 1.3538H 2O + 0.0184SO2

510.07

(7)

Because the required volume of pure retorting gas is 16.57 m3 (18.42 kg), according to the relationship with the coefficient of the chemical reaction equation, the volume and mass of the reactants and products can be calculated and are shown in Table 7.

1060.97

heat requirement is 1060.97 MJ, which is basically equal to the total heat supply needed to maintain the heat balance in the retort. 4.2. Material Balance Calculation. 4.2.1. Material Balance of Ash Trough. As apparent from the description of the structure of SJ-retort in section 2.1, the temperatures of the semi-coke that falls into the trough and out of the trough are 250 and 90 °C, respectively, and 10% water is simultaneously removed with the semi-coke. Because of the evaporation loss of water in the trough, cooling water must be occasionally added to maintain the water seal depth. In the calculation, the sensible heat of semi-coke in the trough is 147.17 MJ, the sensible heat of removed water is 22.08 MJ, and the heat loss of ash trough (20%) is 29.43 MJ. In summary, for each 1000 kg of oil shale retorting, the weight of evaporated water from the trough is 38 kg and the water removed by the semi-coke is 88 kg. The total loss of water of the trough is 126 kg; therefore, a corresponding amount of water should be added to the trough to maintain the balance of water. 4.2.2. Gas Balance of SJ-Retort. Suppose the quantity of heat for 1000 kg of oil shale retorting is Qabsorb and is provided by the combustion of an initial volume of retorting gas and air. After a series of pyrolysis and combustion processes, the retorting gas, N2, CO2, and SO2 are generated from the retort. In this section, a calculation method is presented to analyze the circulation of types of gases during the oil shale retorting process. In fact, various complex physical and chemical reactions occur in the process of oil shale retorting with the material balance, heat balance, and gas balance. To simplify the calculation, the presentation of the calculation method is developed on the basis of the following assumptions: (1) In the initial phase, before the formation of the steady retorting recycle system, the required heat for oil shale retorting is entirely supplied by the combustion of pure retorting gas. In this state, the input gases are a mixture of pure retorting gas and air to provide O2 for combustion. (2) When the reaction continues, the output gases of the retort include pure retorting gas, which is produced by oil shale retorting, N2, which is brought by the input air, and CO2 and SO2, which are generated by the combustion of pure retorting gas and O2. To maintain the pressure balance in the retort and subsequent heat requirement for oil shale retorting, which is supplied by the combustion of retorting gas, part of the output gases is used as a recycle gas for combustion heating and the remaining gases

Table 7. Volumes of Reactants and Products for Pure Retorting Gas Combustion combustion of pure retorting gas needed pure retorting gas O2 air N2 CO2 H2O SO2

a

m3

kg

16.57 24.60 117.16 92.56 17.89 22.43 0.30

18.42 35.15 150.85 115.70 35.15 18.02 0.87

a

The pure retorting gas is the pyrolysate that removes the condensable fraction of oil shale.

We simulate the operation of SJ-retort. According to the change of various types of gas and until the retorting process circulation stabilizes, the following formula is obtained: Vn(output gas) = V1(output gas)(1 + 1/K + 1/K2 + ... + 1/K n − 1) Vn(recycle gas) = Vn − 1(output gas)/K

(8) (9)

where n ≥ 2, K = Voutput retorting gas/Vrecycle retorting gas = 21.07/ 16.57, Vn(output gas) is the volume of output gas (N2, CO2, and SO2) from 2 to n, and Vn(recycle gas) is the volume of recycle gas (N2, CO2, and SO2) from 2 to n. Some gases that exit from SJ-retort are released, and the remaining gases are recycled into the retort to provide heat. According to the above formula, the changes in composition of the input, recycle, release, and output gases are obtained as follows in Tables 8 and 9. As listed in Tables 8 and 9, when the retorting system approaches an equilibrium, that is, when n tends to infinity, the total volume of input gases of the retort is 542 m3, the total volume of output gases is 540 m3, the volume of recycle gases to re-enter the retort is 424 m3, the volume of new air entering the retort is 117 m3, and the volume of release gases is 115 m3. Figure 2 gives the following conclusions: (1) The heat for oil shale retorting is supplied by the combustion of the retorting gas. The required air for pure retorting gas combustion is constant with time. When the retort continues, the volume of the released gases gradually increases and eventually stabilizes. 6377

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Energy & Fuels Table 8. Volume Calculation Results of the Total Input Gases new input air (m3) 1 2 3 4 5 6 7 8 9 10 11 12 13 n

recycle gas (m3)

O2

N2

total

retorting gas

N2

CO2

SO2

total

total input gas (m3)

24.60 24.60 24.60 24.60 24.60 24.60 24.60 24.60 24.60 24.60 24.60 24.60 24.60 24.60

92.56 92.56 92.56 92.56 92.56 92.56 92.56 92.56 92.56 92.56 92.56 92.56 92.56 92.56

117.16 117.16 117.16 117.16 117.16 117.16 117.16 117.16 117.16 117.16 117.16 117.16 117.16 117.16

16.57 16.57 16.57 16.57 16.57 16.57 16.57 16.57 16.57 16.57 16.57 16.57 16.57 16.57

0 72.79 130.04 175.06 210.46 238.30 260.20 277.42 290.96 301.61 309.99 316.57 321.75 340.83

0 14.07 25.13 33.83 40.68 46.06 50.29 53.62 56.24 58.30 59.91 61.19 62.19 65.87

0 0.24 0.42 0.57 0.68 0.77 0.84 0.90 0.94 0.98 1.00 1.03 1.04 1.10

16.57 103.67 172.16 226.03 268.39 301.70 327.90 348.51 364.71 377.46 387.47 395.36 401.55 424.37

133.73 220.83 289.32 343.19 385.55 418.86 445.06 465.67 481.87 494.62 504.63 512.52 518.71 541.54

Table 9. Volume Calculation Results of the Output Gases and Release Gases output gas (m3) 1 2 3 4 5 6 7 8 9 10 11 12 13 n

release gas (m3)

retorting gas

N2

CO2

SO2

total

retorting gas

N2

CO2

SO2

total

21.07 21.07 21.07 21.07 21.07 21.07 21.07 21.07 21.07 21.07 21.07 21.07 21.07 21.07

92.56 165.35 222.60 267.62 303.02 330.86 352.76 369.98 383.52 394.17 402.55 409.13 414.31 433.39

17.89 31.96 43.02 51.72 58.57 63.95 68.18 71.51 74.13 76.18 77.80 79.08 80.08 83.76

0.30 0.54 0.72 0.87 0.98 1.07 1.14 1.20 1.24 1.28 1.30 1.33 1.34 1.40

131.82 218.92 287.41 341.28 383.64 416.95 443.15 463.76 479.96 492.70 502.72 510.61 516.80 539.62

4.50 4.50 4.50 4.50 4.50 4.50 4.50 4.50 4.50 4.50 4.50 4.50 4.50 4.50

19.77 35.31 47.54 57.16 64.72 70.66 75.34 79.02 81.91 84.18 85.97 87.38 88.49 92.56

3.82 6.82 9.19 11.05 12.51 13.66 14.56 15.27 15.93 16.27 16.62 16.89 17.10 17.89

0.06 0.11 0.15 0.18 0.21 0.23 0.24 0.26 0.26 0.27 0.28 0.28 0.29 0.30

28.15 46.74 61.38 72.89 81.94 89.05 94.64 99.05 102.60 105.22 107.37 109.05 110.38 115.25

increases and is eventually equal to the volume of the output gases. Then, an equilibrium between the input and output gases is attained. (3) When the retorting process continues, the volume of the recycle gases gradually increases and eventually stabilizes to a dynamic balance. 4.2.3. Materials Balance of SJ-Retort. Figure 3 shows a simple diagram of the balance during the process of Myanmar oil shale retorting. The input materials of the retort clearly include oil shale, air, recycle gases, and supplementary water of the trough. The output materials are output gases, shale oil, water vapor, semicoke, and the water from the trough. The respective weight is shown in Table 10. In Table 10, when the retort achieves a stable operation, the total input is approximately 1854 kg, the total output is approximately 1850 kg, and the loss is approximately 4 kg, which can basically maintain the material balance in the retort. Figure 2. Types of gases gradually tend to balance during the retorting process.

5. CONCLUSION To study the feasibility of Myanmar oil shale processing by SJretort, this paper calculated the material and heat balance of the retorting process. According to the result of conducted analyses, it was found that, when the retort reaches a stable operation, the total heat requirement is 1060.97 MJ and the total heat provided is 550.90 MJ, obtained from the sensible

Finally, they achieve a dynamic balance against the new input air. (2) The retort output gases have an increasing trend and eventually stabilize. The sum of the new input air and recycle gas volumes is the volume of the input gases, which gradually 6378

DOI: 10.1021/acs.energyfuels.6b01178 Energy Fuels 2016, 30, 6373−6380

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Energy & Fuels Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors are grateful for the financial support from the National Basic Research Program of China (973 Program, 2014CB744302), the Taishan Scholar Constructive Engineering Foundation of Shandong Province, China (ts20120518), and scientific research fund of China University of PetroleumBeijing (2462015YQ0601).

■

Figure 3. Diagram of the materials and heat balance of oil shale retorting.

Table 10. Materials Balance of SJ-Retort for Myanmar Oil Shale Processing (1000 kg, Received Basis) input

kg

(1) oil shale (2) air (117 m3) (3) recycle gases (424 m3) (4) supplementary water of trough

1000 151 577 126

(1) (2) (3) (4)

1854

(5) water taken out from trough (6) loss total

total

output output gases (540 m3) shale oil water vapor semi-coke

kg 734 57 91 880 88 4 1854

heat of its pyrolysates. Thus, the complement heat should be 510.07 MJ, which is provided by 16.57 m3 retorting gas combustion, and 33.26% surplus retorting gas can be obtained when 1000 kg of oil shale is processed, which indicates that the high-calorie heat of the retorting gas combustion can satisfy the requirement of Myanmar oil shale retorting and the Myanmar oil shale can be processed by SJ-retort theoretically. Simultaneously, a new concise method was proposed to calculate the gas circle balance. When eqs 8 and 9 are combined with the original volume of retorting gas and combustion reaction equation, the volume of the output gases, release gases, and recycle gases can be calculated easily when the retort achieves a stable operation, which can provide preliminary information about the oil shale processed by a retort. However, the feasibility depends upon multi-factors, and a pilot-scale test must be performed before operation. In fact, Yaojie oil shale has been successfully processed by SJretort.15,16,26 The result of the pilot-scale test is consistent with the prior theoretical calculation, which further verifies the accuracy of the calculation method. Because Yaojie oil shale was successfully processed by SJ-retort, the processing of Myanmar oil shale might also be feasible. In addition, this retorting process has been widely applied in Shanxi, Inner Mongolia, and other provinces of China, and the complete set of equipment has been exported to Kazakhstan and put into operation.

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DOI: 10.1021/acs.energyfuels.6b01178 Energy Fuels 2016, 30, 6373−6380

Article

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DOI: 10.1021/acs.energyfuels.6b01178 Energy Fuels 2016, 30, 6373−6380