Possibilities of Climate Control of Poultry Complexes through Co-Combustion of Poultry Waste–Solid Biomass for Agriculture in Romania

Abstract

The dynamics of poultry waste co-combustion with solid biomass has been theoretically and experimentally analyzed by authors in several works. The current work is focused on a case study regarding the energy recovery from poultry waste in order to use it for heating a 1000 m³ chicken rearing complex, considering the specific climatic conditions in Romania. Even if biomass has significant national potential, there are only a few experimental incentives in our country to use it for energy production. Since poultry manure is characterized by high moisture and low calorific value, its co-combustion with solid biomass was chosen. Thus, laboratory experiments involving the combustion of 20–30% poultry waste were carried out on a 55 kW pilot boiler. This is an environmentally friendly and low-cost approach. The tests showed that phosphorus and potassium are concentrated by the combustible mass disappearance in the ash (P = 3.2–5.5% and K = 2.2–3.8%), leading to the conclusion that it represents a much more valuable fertilizer than raw waste, since it is lighter and much easier to store, transport, and spread over the agricultural area. The poultry waste mix with solid biomass was taken into account for heating a chicken rearing hall module by considering the needs of each period (cycle) in the development of the chicken-bird flow in accordance with a temperate-continental climate, such as Romania’s climate. The resulting annual fuel consumption is 53.27 t. This quantity represents 42.60 t of biomass and 10.67 t of poultry manure. The co-combustion showed pollutant emissions within the legal limits and no presence of ammonia, which was incinerated on the biomass layer surface.

1. Introduction

The recent energy crisis, as well as the increasing emphasis on the circular economy, highlighted even more the necessity of producing green energy and reusing or minimizing waste. In this context, it is necessary to pay special attention to the use of agricultural, industrial, and household waste in energy production. The present work is focused on using poultry waste to generate energy to be used for heating a poultry rearing hall.

Different techniques and technologies [1], such as anaerobic digestion [2,3], hydrogenation, pyrolysis, and gasification [4,5], can be used for energy recovery and for the reduction of secondary products of poultry farms. In rural areas of Europe, biogas plants using biomass and animal waste are often found [6,7].

In Romania, there is huge biomass potential, but with a low degree of use. According to [8], it represents 51.61% of the entire renewable energy source in the country. In addition, Romania has a developed poultry meat production industry, resulting in significant amounts of poultry litter, which is only used as fertilizer [9]. Furthermore, there are only a few experimental incentives to use it for thermal energy production [8]. As shown by previous research [10], the use of poultry manure to produce energy is a cleaner valorization of this waste compared to its use as fertilizer. This approach is also characterized by other advantages, such as harmful emissions reduction, lower environmental impact [10], and lower costs when used at its source location, considering that transport costs are eliminated.

In this context, this paper addresses the efficient generation of energy through the co-combustion process of raw poultry droppings with solid biomass (woody and agricultural) for heating a 1000 m³ chicken rearing hall. As a result of this process, poultry waste can be used as fertilizer or can be semi-ecologically stored in large quantities. After combustion, the amount of stored poultry waste is reduced, resulting in ash enriched with phosphorus and calcium, which is easy to handle and distribute to agricultural users.

The direct combustion of poultry waste proved to be very difficult in the conducted experiments due to its negative energy characteristics (low calorific value and high humidity). The solid biomass co-combustion technology was chosen considering that both components have the same aggregation state and the high thermal inertia of the burning biomass bed. The final fractions of poultry waste and biomass resulted after a long series of experiments.

The co-combustion technology of poultry waste with solid biomass is not addressed in the literature. As a novelty, fixed or mobile bed combustion technology was used (obtained by moving the grate bars of the combustion plant). This technology limits the power of the combustion plant, but the possibility of placing several plants in parallel is considered.

Another possibility to reduce or eliminate poultry waste is represented by applying an aerobic treatment before spreading the waste on the field. The poultry litter composting process [11] transforms the soluble nutrients into stable organic forms [12]. In addition, aerobic treatment reduces the waste moisture content [13]. To obtain the organic fertilizer used for soil fertilization [14], both poultry waste [15] and manure [16] can be composted. It should be noted that they can also be composted in a mixture with other organic products, including bio-waste [17,18].

In addition to obtaining energy [19,20] or biofuels [21,22], poultry waste treatment is also necessary in order to ensure environmental protection, as well as alternative fertilizers to the chemical ones [23,24], to reduce the eutrophication of water bodies [25,26], the pathogen contamination risk [27], heavy metals, or arsenic [28]. The value of poultry manure-derived biochar as soil fertilizer is shown by different studies analyzing its effects on various cultures like tomatoes [29], maize, and soybeans [26].

The present research aims to achieve two main objectives. The first is the management of avian waste by reducing the amount that must be stored within poultry complexes. The second aim is represented by the valorization and recovery of energy from solid biomass and avian waste, through the production of thermal energy [30,31,32,33], used locally for the air conditioning of poultry complexes. The research also responds to the current European requirements regarding both pollution reduction and renewable energy production and use, especially for self-consumption.

The research has considered the possibility of using poultry droppings to produce energy for heating poultry houses [33,34,35]. As manure is very moist, as shown in previous studies, its combustion along with woody biomass (co-combustion) was considered [36,37]. The use of poultry droppings for heating the technological halls has a double representativeness, the first being with reference to energy, including savings in the fuel balance, while the second is reflected in the pollution reduction. The calculations were made on the basis of the “Poultry housing systems. Farm standards” manual [38], recommended for use within the National Rural Development Program 2007–2013 and approved by all the relevant forums and ministries in Romania. The heating process is closely related to ventilation, which is indispensable for poultry life [39,40].

The data from [37] were compared and correlated with those obtained from the operation of a poultry complex containing the following:

• Eighteen identical production halls, with an area of 910 m² each;
• Heating installations with air heaters for twelve halls, two of 100 kW each for one hall, and radiant heating for six halls (13 units of 12 kW each for one hall);
• Ventilation with 6 units of 35,000 m³/h each (1.5 kW power).

In the case study, a calculation unit (a poultry house module) with a volume V = 1000 m³ (an area of S = 320 m², and a height H = 3.1 m, respectively) was considered.

2. Determination of the Thermal Power for Heating

According to the design data in [37], the thermal power for heating a hall must fall within the limit of 40 W/m³. The calculation was made for a hall module of 1000 m³, so the thermal power of the installation will be the following:

$$P_t=40·1000=\mathrm{40,000} \mathrm{W}=40 \mathrm{k}\mathrm{W},$$

(1)

For the hot water plant used for heating, an efficiency of 88% (ƞ = 0.88) and a standard fuel composed of biomass and poultry waste were considered [41]. This fuel has been tested experimentally. For this purpose, a 55 kW pilot boiler was used, equipped with a fixed combustion grate [2].

In the studied case, the poultry droppings taken from the hall have about 10% biomass (wood chips, sawdust, or straw). The laboratory analyses carried out within the Thermotechnics Department of the National University of Technical Sciences Politehnica Bucharest (UNSTPB), as well as the elemental analysis, revealed the following values range for the waste composition: carbon content $C^i=12.3–22.5\mathrm{\%}$; hydrogen content $H^i=4.3–5.2\mathrm{\%}$; fuel sulfur content $S_c^i=1.7–2.0\mathrm{\%}$; oxygen content $O^i=35.1–37.4\mathrm{\%}$; nitrogen content $N^i=1.4–2.3\mathrm{\%}$; ash content $A^i=6.1–12.9\mathrm{\%}$; and humidity content $W^i=36.0–40.0\mathrm{\%}$.

The fuel is a mixture of raw poultry waste, as taken from the chicken rearing hall, and solid biomass. The rest of the poultry waste that was not used for co-combustion followed the classical greening path.

The standard fuel considered comprises 80% woody biomass with a calorific value of 14,350 kJ/kg and 20% poultry waste with a calorific value of 6000 kJ/kg, the final calorific value of the mixture being [2]:

$$H_i^i=0.8·\mathrm{14,350}+0.2·6000=\mathrm{12,500}\frac{\mathrm{k}\mathrm{J}}{\mathrm{k}\mathrm{g}}$$

(2)

The tested combustion technology involved dosing poultry litter over the burning biomass bed (Figure 1).

Figure 1. Images of the combustion process inside the hearth of the 55 kW pilot boiler at different times of the experiment. (a) Minute 2. (b) Minute 29.

The efficiency of the boiler η varied in the range of 79–89%, depending on the mass fuel loading and excess air. For the fuel consumption calculation, the value η = 88 was considered.

Nominal fuel consumption was calculated as follows:

$$B_N=\frac{P_t}{\mathrm{ƞ} ·{ H}_i^i}=\frac{40}{0.88·\mathrm{12,500}}=0.00363\frac{\mathrm{k}\mathrm{g}}{\mathrm{s}}=13\frac{\mathrm{k}\mathrm{g}}{\mathrm{h}},$$

(3)

The experiments indicated the need for a density as low as possible in the layer, which can be obtained through dimensional control, so that air penetration is facilitated. Poultry litter was positioned on top of the biomass layer. The temperature in the layer was monitored with the help of thermocouples, and the combustion products (pollutants) were measured using a TESTO 350 device. The air excess λ was within the limits of 1.4–2.1, and the carbon monoxide CO emission was between 800 and 900 ppm. NO_x emissions were below 150–170 ppm.

Figure 2 shows the experimental test rig used for performing the envisaged tests, with the pilot boiler equipped with all the measuring and control devices [2,37,42].

Figure 2. Pilot test rig—the 55 kW boiler from the Thermo-technical Laboratory of the Mechanics and Mechatronics Faculty, UNSTPB. (a) Diagram of the pilot test rig cross-section; (b) front diagram of the pilot test rig.

The experiment was carried out at laboratory scale with the help of a pilot test rig involving a furnace/boiler for residential heating, the Multiplex CL 50 model, with a fixed grate and a thermal power of 55 W, from the Thermo-technical Laboratory of the Mechanics and Mechatronics Faculty, UNSTPB. The boiler is also equipped with a liquid fuel burner, which is necessary for starting operations with solid fuel or for full operation with light fuels.

Regarding the energy efficiency, Figure 3 shows the installation energy yield variation with the exhaust temperature of the combustion gases at the chimney. The obtained values fall within the recommended range for the respective fuel quality. If the energy yield is correlated with the pollutant emissions previously presented, the result is a high-performance technology.

Figure 3. Energy yield variation with the exhaust temperature of the released combustion gases.

Fuel Consumption

The produced necessary heat must satisfy the heat removal from the hall through ventilation [43]. Figure 4 shows the calculation scheme (the considered reference temperature was 0 °C).

Figure 4. Calculation scheme for the required heat. Where $Q_{ext}$—heat exchanged with the outside environment; $Q_{vent}$—heat removed through ventilation; $Q_{air}$—the heat introduced by the fresh air; $Q_t$—heat introduced with the heating agent.

The recommended ventilation system capacity is 0.5–6 (m³/h)/kg, the lower values being for the winter days with the lowest temperatures [38].

The temperature in the technological hall depends on the size of the poultry (their age), and the following values are recommended (an 8-week cycle was considered) [38].

An eight-week cycle (56 days) ends on average with 4 days when the temperature must be raised to 33 ℃ for an ecological cleaning. For organic chicken rearing, a maximum amount of 25 kg of chicken meat per square meter hall was considered. This figure assumes the chicken is growing on the ground under permanent litter conditions in an extensive rearing system (CE1538/91).

The ventilated flow per unit volume (m³/s)/m³, defined by reference to the useful volume $V_v$/(0.7), varies within the following limits:

• Week 1: 0.007 (m³/s)/m³;
• Week 6–8: 0.0028–0.0042 (m³/s)/m³.

Depending on the external environment temperature value $t_{ex}$, the required heat $Q_{real}$ will have the following value compared to the thermal power $P_t$ ($t_v$ being the discharged temperature):

$$Q_{real}=\frac{P_t}{t_v+t_{ex}}\left(t_v-t_{ex}\right) \mathrm{k}\mathrm{W}$$

(4)

For the ventilation temperature, refer to the data in Table 1, and for $t_{ex}$, refer to the statistical meteorological data. Figure 5 shows the heat requirement according to the correlation between the growth cycle and the outside temperature (for the temperate continental climate in southern Romania, the minimum calculation temperature is considered to be −12 °C).

Table 1. Recommended environmental conditions for a poultry rearing cycle.

Week	Recommended Temperature, °C	Humidity, %
1	33	50–70
2	29	50–60
3	25	50–70
4	22	35–75
5	20	35–75
6	18	35–75
7	18	35–75
8 *	18	35–75

* 2007/43/CE.

Figure 5. The variation of the heat requirement depending on the external environment temperature, $t_{ex}$: a—week 6–8; b—week 5; c—week 4; d—week 3; e—week 2; f—week 1.

The heat required to heat the halls for a certain outside temperature $t_{ex}$ imposed by relation (4) will have to be checked with the heat required to achieve the ventilation temperature. The corrections will allow the modification of the ventilation flow rate, preferably towards the higher values presented [43].

The heating required by the different stages of bird growth in the temperate continental climate conditions does not depend on the used fuel, but on achieving the heat for the imposed power norms, all in correlation with the thermal effect of the ventilation (the nature of the fuel only influences the consumption per unit of time). This fuel consumption was calculated for the characteristics of the poultry waste–solid biomass mixture.

The average monthly temperature for a region in the south of Romania was used in the calculations. These values are presented in the temperature graphs. For the temperate continental climate, the viability of the heating installation with a thermal power of 40 W/m³ and the existence of a relatively long non-heating period were verified.

3. Fuel Consumption of Poultry Manure–Solid Biomass for an Annual Growth Cycle

The calculation was carried out for a period of 1 year, starting with the coldest period of the year, with the 1st week of chicken growth starting on 1 January. The temperature evolution graph is presented in Figure 6 (the area around the city of Bucharest was considered).

Figure 6. The outdoor temperature during the first period of poultry growth.

3.1. The First Poultry Growth Cycle

• Fuel consumption for the first chick rearing cycle is calculated as follows:

  $$B_{I }=B_{1-4}+B_{5-8}=9194 \mathrm{k}\mathrm{g}$$

  where $B_{1 }÷B_8$ represents the weekly fuel consumption.

• Checking the heat removed by ventilation to the outside environment.

The calculations were performed based on relation (4); the results are presented in Table 2.

Table 2. Ventilation heat for growth cycle I.

Week	Annual Period	${\mathit{t}}_{\mathit{e}\mathit{x}}$ [°C]	${\mathit{t}}_{\mathit{v}}$ [°C]	Volumetric Mass Loading [kg/m3]	The Ventilation Coefficient [m3/h/kg]	$\mathbf{Ventilation} {\mathit{Q}}_{\mathit{v}}$ [kW]	$\mathbf{Average} \mathbf{Fuel} \mathbf{Consumption} \overline{\mathit{B}}$ [kg]
1	1.I–7.I	−2.4	33	2	0.50	8.87	487
2	8.I–14.I	−2.4	29	3	0.50	12.08	663
3	15.I–21.I	−2.4	25	4	0.55	15.19	834
4	22.I–28.I	−2.4	22	5	0.60	18.68	1025
5	29.I–4.II	−0.1	20	6	0.7	21.49	1180
6	5.II–11.II	−0.1	18	6.5	0.7	21.02	1154
7	12.II–18.II	−0.1	18	7.0	0.7	22.57	1239
8	19.II–25.II	−0.1	18	7.5	0.7	24.25	1331
Cleaning	26.II–1.III	−0.1	18	-	-	24.25	761
Total							8674

The total fuel consumption for the first poultry rearing cycle is: B_Itot = 17,868 kg, out of which 51.45% is for heating and 48.55% is for ventilation.

3.2. The Second Poultry Growth Cycle

Figure 7 shows the variation of the outside temperature for the 8 weeks necessary for poultry growth that comprise the second growth cycle.

Figure 7. The outdoor temperature during the second period of poultry growth.

The fuel consumption for heating is presented in Table 3, and for the ventilation operation in Table 4.

Table 3. Fuel consumption for heating during the second period of poultry growth.

Week	Annual Period	${\mathit{t}}_{\mathit{e}\mathit{x}}$ [°C]	${\mathit{t}}_{\mathit{v}}$ [°C]	Heat for Heating Q [kW]	Fuel Consumption Per Unit of Time [kg/s]	Fuel Consumption Per Week [kg]
1	2.III–8.III	4.8	33	25.0	0.0022	1372
2	9.III–15.III	4.8	29	21.5	0.0019	1147
3	16.III–22.III	4.8	25	17.9	0.0015	960
4	23.III–29.III	4.8	22	15.2	0.0013	785
5	30.III–5.IV	11.3	20	10	0.0009	549
6	6.IV–12.IV	11.3	18	5.9	0.0005	302
7	13.IV–19.IV	11.3	18	5.9	0.0005	302
8	20.IV–26.IV	11.3	18	5.9	0.0005	302
-	27.IV–30.IV	11.3	18	5.9	0.0005	172
Total						BII = 5891 kg

Table 4. Ventilation heat for second growth period.

Week	Annual Period	${\mathit{t}}_{\mathit{e}\mathit{x}}$ [°C]	${\mathit{t}}_{\mathit{v}}$ [°C]	Volumetric Mass Loading [kg/m3]	The Ventilation Coefficient [m3/h/kg]	$\mathbf{Ventilation} {\mathit{Q}}_{\mathit{v}}$ [kW]	$$\begin{gathered} \mathbf{Average} \mathbf{Fuel} \\ \mathbf{Consumption} \overline{\mathit{B}} \end{gathered}$$ [kg]
1	2.III–8.III	4.8	33	2	0.6	8.56	470
2	9.III–15.III	4.8	29	3	0.7	13.04	715
3	16.III–22.III	4.8	25	4	0.8	19.87	1091
4	23.III–29.III	4.8	22	5	0.9	19.86	1091
5	30.III–5.IV	11.3	20	5	1.0	13.39	735
6	6.IV–12.IV	11.3	18	7	1.1	13.24	730
7	13.IV–19.IV	11.3	18	8	1.2	16.50	906
8	20.IV–26.IV	11.3	18	8.5	1.3	18.66	1024
Cleaning	27.IV–30.IV	16.7	18	-	-	18.66	732
Total							7494

3.3. The Third Poultry Growth Cycle

Figure 8 shows the variation of the outside temperature necessary for the 8-week poultry growth corresponding to this period.

Figure 8. The outdoor temperature during the third period of poultry growth.

Fuel consumption for heating and ventilation is presented in Table 5 and Table 6, respectively.

Table 5. Fuel consumption for heating during the third period of poultry growth.

Week	Annual Period	${\mathit{t}}_{\mathit{e}\mathit{x}}$ [°C]	${\mathit{t}}_{\mathit{v}}$ [°C]	Heat for Heating Q [kW]	Fuel Consumption Per Unit of Time [kg/s]	Fuel Consumption Per Week [kg]
1	1.V–7.V	16.7	33	14.48	0.0013	795
2	8.V–14.V	16.7	29	10.93	0.0001	600
3	15.V–21.V	16.7	25	7.37	0.0006	362
4	22.V–28.V	16.7	22	4.71	0.0004	241
5	29.V–4.VI	20.2	20	0	0	0
6	5.VI–11.VI	20.2	18	0	0	0
7	12.VI–18.VI	20.2	18	0	0	0
8	19.VI–25.VI	20.2	18	0	0	0
Cleaning	26.VI–30.VI	22	18	0	0	0
Total						BIII = 1998 kg

Table 6. Ventilation heat for the third period of poultry growth.

Week	Annual Period	${\mathit{t}}_{\mathit{e}\mathit{x}}$ [°C]	${\mathit{t}}_{\mathit{v}}$ [°C]	Volumetric Mass Loading [kg/m3]	The Ventilation Coefficient [m3/h/kg]	$\mathbf{Ventilation} {\mathit{Q}}_{\mathit{v}}$ [kW]	$$\begin{gathered} \mathbf{Average} \mathbf{Fuel} \\ \mathbf{Consumption} \overline{\mathit{B}} \end{gathered}$$ [kg]
1	1.V–7.V	16.7	33	2	0.6	5.02	275
2	8.V–14.V	16.7	29	3	0.7	6.62	363
3	15.V–21.V	16.7	25	4	0.8	6.81	373
4	22.V–28.V	16.7	22	5	0.9	6.12	336
5	29.V–4.VI	20.2	20	6	3	0	0
6	5.VI–11.VI	20.2	18	7	3	0	0
7	12.VI–18.VI	20.2	18	8	3	0	0
8	19.VI–25.VI	20.3	18	8.5	3	0	0
Cleaning	26.VI–30.VI	20.3	18	-	-	0	0
Total							1347

3.4. The Fourth Poultry Growth Cycle

Figure 9 shows the variation of the outside temperature for the 8 weeks of poultry growth for the fourth cycle.

Figure 9. The outdoor temperature during the fourth period of poultry growth.

Fuel consumption for heating and ventilation is presented in Table 7 and Table 8, respectively.

Table 7. Fuel consumption for heating during the fourth period of poultry growth.

Week	Annual Period	${\mathit{t}}_{\mathit{e}\mathit{x}}$ [°C]	${\mathit{t}}_{\mathit{v}}$ [°C]	Heat for Heating Q [kW]	Fuel Consumption Per Unit of Time [kg/s]	Fuel Consumption Per Week [kg]
1	31.VI–6.VII	22	33	9.77	0.0008	483
2	7.VII–13.VII	22	29	6.22	0.0005	302
3	14.VII–20.VII	22	25	2.66	0.0002	120
4	21.VII–27.VII	22	22	0	0	0
5	28.VII–3.VIII	21.2	20	0	0	0
6	4.VIII–10.VIII	21.2	18	0	0	0
7	11.VIII–17.VIII	21.2	18	0	0	0
8	18.VIII–24.VIII	21.2	18	0	0	0
Cleaning	25.VIII–28.VIII	21.2	18	0	0	0
Total						BIV = 905 kg

Table 8. Ventilation heat for the fourth period of poultry growth.

Week	Annual Period	${\mathit{t}}_{\mathit{e}\mathit{x}}$ [°C]	${\mathit{t}}_{\mathit{v}}$ [°C]	Volumetric Mass Loading [kg/m3]	The Ventilation Coefficient [m3/h/kg]	$\mathbf{Ventilation} {\mathit{Q}}_{\mathit{v}}$ [kW]	Average Fuel Consumption $\overline{\mathit{B}}$ [kg]
1	31.VI–6.VII	22	33	2	0.6	2.56	140
2	7.VII–13.VII	22	29	3	0.7	2.85	156
3	14.VII–20.VII	22	25	4	0.8	1.86	102
4	21.VII–27.VII	22	22	5	0.9	0	0
5	28.VII–3.VIII	21.2	20	6	3	0	0
6	4.VIII–10.VIII	21.2	18	7	3	0	0
7	11.VIII–17.VIII	21.2	18	8	3	0	0
8	18.VIII–24.VIII	21.2	18	8.5	3	0	0
Cleaning	25.VIII–28.VIII	21.2	18	-	-	0	0
Total							398

3.5. The Fifth Poultry Growth Cycle

Figure 10 shows the variation of the outside temperature for the 8 weeks of poultry growth for the climate of the fifth growth cycle.

Figure 10. The outdoor temperature during the fifth period of poultry growth.

Fuel consumption for heating and ventilation is presented in Table 9 and Table 10, respectively.

Table 9. Fuel consumption for heating during the fifth period of poultry growth.

Week	Annual Period	${\mathit{t}}_{\mathit{e}\mathit{x}}$ [°C]	${\mathit{t}}_{\mathit{v}}$ [°C]	Heat for Heating Q [kW]	Fuel Consumption Per Unit of Time [kg/s]	Fuel Consumption Per Week [kg]
1	29.VIII–4.IX	16.9	33	14.31	0.001	600
2	5.IX–11.IX	16.9	29	10.75	0.0009	543
3	12.IX–18.IX	16.9	25	8.08	0.0007	422
4	19.IX–25.IX	16.9	22	4.53	0.0004	241
5	26.IX–2.X	10.8	20	8.17	0.0007	543
6	3.X–9.X	10.8	18	6.4	0.0005	300
7	10.X–16.X	10.8	18	6.4	0.0005	300
8	17.X–23.X	10.8	18	6.4	0.0005	300
Cleaning	24.X–28.X	10.8	18	6.4	0.0005	216
Total						BV = 3465 kg

Table 10. Ventilation heat for the fifth period of poultry growth.

Week	Annual Period	${\mathit{t}}_{\mathit{e}\mathit{x}}$ [°C]	${\mathit{t}}_{\mathit{v}}$ [°C]	Volumetric Mass Loading [kg/m3]	The Ventilation Coefficient [m3/h/kg]	$\mathbf{Ventilation} {\mathit{Q}}_{\mathit{v}}$ [kW]	Average Fuel Consumption $\overline{\mathit{B}}$ [kg]
1	29.VIII–4.IX	16.9	33	2	0.6	3.75	181
2	5.IX–11.IX	16.9	29	3	0.7	6.51	357
3	12.IX–18.IX	16.9	25	4	0.8	6.64	364
4	19.IX–25.IX	16.9	22	5	0.9	5.89	323
5	26.IX–2.X	10.8	20	6	1.0	10.73	589
6	3.X–9.X	10.8	18	7	1.1	14.22	780
7	10.X–16.X	10.8	18	8	1.2	17.74	974
8	17.X–23.X	10.8	18	8.5	1.3	20.42	1121
Cleaning	24.X–28.X	10.8	18	-	-	20.42	641
Total							5330

The yellow line in Figure 10 shows the average outdoor temperature in accordance with the data in Table 9.

3.6. The Sixth Growth Cycle of the Poultry

Figure 11 shows the variation of the outside temperature for the 8 weeks of poultry growth, for the climate of the sixth growth cycle.

Figure 11. The outdoor temperature during the sixth period of poultry growth.

Fuel consumption for heating and ventilation is presented in Table 11 and Table 12, respectively.

Table 11. Fuel consumption for heating during the sixth period of poultry growth.

Week	Annual Period	${\mathit{t}}_{\mathit{e}\mathit{x}}$ [°C]	${\mathit{t}}_{\mathit{v}}$ [°C]	Heat for Heating Q [kW]	Fuel Consumption Per Unit of Time [kg/s]	Fuel Consumption Per Week [kg]
1	29.X–4.XI	5.2	33	24.71	0.0020	1200
2	5.XI–11.XI	5.2	29	21.15	0.0019	1176
3	12.XI–18.XI	5.2	25	17.60	0.0016	966
4	19.XI–25.XI	5.2	22	14.93	0.0013	785
5	26.XI–2.XII	0.2	20	13.15	0.0011	664
6	3.XII–9.XII	0.2	18	15.82	0.001	604
7	10.XII–16.XII	0.2	18	15.82	0.001	604
8	17.XII–23.XII	0.2	18	15.82	0.001	604
Cleaning	24.XII–31.XII	0.2	18	15.82	0.001	172
Total						BV = 6775 kg

Table 12. Ventilation heat for the sixth period of poultry growth.

Week	Annual Period	${\mathit{t}}_{\mathit{e}\mathit{x}}$ [°C]	${\mathit{t}}_{\mathit{v}}$ [°C]	Volumetric Mass Loading [kg/m3]	The Ventilation Coefficient [m3/h/kg]	$\mathbf{Ventilation} {\mathit{Q}}_{\mathit{v}}$ [kW]	Average Fuel Consumption $\overline{\mathit{B}}$ [kg]
1	29.X–4.XI	5.2	33	2	0.5	7.13	391
2	5.XI–11.XI	5.2	29	3	0.6	11.00	604
3	12.XI–18.XI	5.2	25	4	0.7	10.78	591
4	19.XI–25.XI	5.2	22	5	0.7	17.24	946
5	26.XI–2.XII	0.2	20	5.5	0.7	19.56	1074
6	3.XII–9.XII	0.2	18	6	0.7	19.18	1053
7	10.XII–16.XII	0.2	18	6.5	0.7	20.78	1141
8	17.XII–23.XII	0.2	18	7	0.7	22.38	1228
Cleaning	24.XII–31.XII	0.2	18	-	-	22.38	350
Total							7378

The graph in Figure 12 highlights the variation of fuel consumption over the months of a year.

Figure 12. Monthly variation of fuel consumption.

The annual fuel consumption is 53.27 t. This amount represents 42.60 t of biomass and 10.67 t of poultry manure.

According to the experiments carried out, the amount of manure that can be burned in co-combustion with woody biomass can increase up to a mass proportion of 30% when it reaches 16 t (woody biomass decreasing to 37.27 t).

The performed calculations indicate that the bird droppings register a significant decrease (of around 30%) following the co-combustion with solid biomass, and this represents an advantage for the environment. Regarding the quality of the air discharged from the halls, the proposed technology does not make any changes. In this phase, the authors have not extended the research in order to perform a rigorous calculation from an economic point of view. Instead, it was intended to validate the proposed solution. This scope was achieved, and it was shown that it ergonomizes the waste processing costs (drying, pelletizing, etc.), as well as storage and transport in ecological conditions; these costs are significant and cannot be neglected.

The calculations showed that the installed power of 40 W/m³ recommended by the norms of the Romanian Ministry of Agriculture satisfied all the annual periods in relation to the climatic conditions. According to the statistical data from [38], reproduced below (Table 13), the droppings when raising broilers represent 3 t for one cycle per 1000 birds. All figures are calculated for 1000 birds during a production cycle [38].

Table 13. Statistical data on the amount of manure in poultry farming [38].

Production Type	Manure with Straw Bedding		Manure with Wood Chip Litter		Manure with Peat or Sawdust Bedding
	m3	t	m3	t	m3	t
Laying hens	103.0	67.0	90.0	68.0	90.0	72.0
Chicks	29.0	15.0	17.0	9.0	17.0	9.5
Broilers	10.0	3.0 *	7.0	3.0 *	7.0	3.3

* data used in the calculations within the study model.

For the studied model, the amount of chicken meat obtained for one cycle is 8.5 kg/m³, which corresponds to an active volume of 700 m³ of 5950 kg/cycle. If the average weight of the birds at slaughter is 2.1 kg, this results in a total of 28,000 birds/cycle. This quantity will correspond to a quantity of 8.4 t manure/cycle. For six annual cycles, the amount of manure (including the vegetable bed) will be 50.4 t/year. This amount of poultry droppings is higher than the 16 t/year required for heating in the analyzed version of wood biomass co-combustion. The remaining amount of manure will follow a storage/drying cycle and will be used as agricultural fertilizer.

The ash resulting from the combustion of the poultry waste and solid biomass mixture registers a mineral material concentration. In this respect, a sensitive increase in phosphorus and potassium is noted. Compared to the ash obtained from biomass, the increase due to poultry waste is about 6–10 times for phosphorus and about 2–2.5 times for potassium. Pulverulent in nature, ash can be easily stored, handled, and spread as a pre-fertilizer.

4. Validity of the Calculation Model for a Unit of 1000 m³

The validation of the analysis was carried out using data from a commercial company that includes 18 identical production halls with different heat sources, each hall having a useful area of 910 m² (2700 m³).

For radiant-heated halls, the installed (thermal) power per unit volume is Q = 55 W/m³. Halls were heated with air heaters with Q = 74 W/m³. Both values are above the one determined in the carried-out study, but within close limits.

In the calculation model, for the ventilation period, the air flow has a value of 1.2 (m³/h)/m³. The higher ventilation value was imposed by the norms in [38]. The effective heat for heating was 30–34 W/m³, similar to the calculations for heating by co-combustion of poultry manure–solid biomass [37].

The solution for chicken intensive rearing hall heating through the co-combustion of poultry waste–solid biomass represents an ecological solution to CO₂ emissions. It can replace heating methods like using fossil fuels, or even electric heaters. For the current period, characterized by high energy price dynamics, no economic study has been carried out. Still, biomass has the lowest price as a primary energy source.

5. Conclusions

The elaborated study presents details regarding the heat requirement, including the external environment temperature and the ventilation required during a year, which includes six periods of 8 weeks each for raising chickens for meat.

The calculation model included a hall with a volume of 1000 m³, out of which 700 m³ are useful.

From a thermal point of view, the limit power of 40 W/m³ for chicken rearing halls proved sufficient for the temperate continental climate in Romania. This justifies the approach of reducing the installed power in old poultry complexes, together with modernization operations.

The necessary heat required solid fuel consumption, consisting of a mixture of 80% woody biomass and 20% wet poultry manure. The calculations showed an excess of poultry manure compared to the energy requirement. The consumption was directly influenced by the temperature of the external environment and the ventilation temperature, characterized by the air temperature at the exit from the hall, in correlation with the mass volumetric loading of meat in each week of the growth period. As a rule, ventilation with a flow as high as possible is aimed at. For the climate in Romania, as the calculations showed, the flow will only be able to vary in the range of 0.6–1.3 (m³/h)/kg, in order to fit the heat discharged within the limits of the one received, corresponding to the installed thermal power (recommended values are in the range of 0.5–5 (m³/h)/kg).

The results of the present work, based on experimental data and on thermal calculations in accordance with [38], led to the conclusion that the air conditioning solution for poultry farms based on the co-combustion of poultry waste with solid biomass is a viable solution [42]. The proposed technology leads to savings in the cost of air conditioning operations, along with ecological effects by reducing the amount of waste left in storage.